I posted the "anti-McCullough" statement and didn't follow up. My apologies, work has been picking up and this topic requires a rather lengthy post to explain it properly.
The issue of Caucasian/Asian dating patterns is a very sensitive issue in some parts of the Asian-American community. The situation is somewhat comparable to the Black Male/White Female dating issues, which generates quite a bit of anger within the African-American female population. It's difficult to discuss because any Asian male speaking on the issue immediately opens himself up to the charge that he's a whiner and that's why Asian females won't date him. At the same time the imbalance in dating patterns is absolutely huge, particularly among the college-educated crowd. In my personal circle of friends who I went to college with, 80% of the Asian females are married to White males. Unscientific observations of the college population in several California universities leads me to guess that there are at least twice as many (and probably as much as three times as many) Asian females dating White males as Asian females dating Asian males (that's in the general college population, if you hang out at the university "international" center or first generation Asian organizations you'll see different numbers). The number of Asian males dating White females account for only a small fraction of couples and can be almost completely discounted. While my evidence is largely anecdotal, I did see a talk by an Asian female professor from UCLA who worked in the Asian-American Mental Health Institute on this issue. She reported (again anecdotally) that virtually none of her Asian male friends were dating and all her Asian female friends were dating non-Asian males -- she herself was dating an African American.
From what I have seen, contrary to Jason's posting, dating patterns in the Asian community do not support the idea that the main cause is "socially maladjusted" Asian males (at least as far as we are assuming only first generation Asian males are maladjusted). If this were the case, we would expect that the out marriage rate would be highest among first generation Asians where the men were maladjusted, but that as Asians reached second and third generation the effects would go away. In fact, the pattern seems to be inverted. First-generation Asian men and women marry each other at a much greater rate than second and third-generation. I believe that this effect is caused in part because cultural ties in the first-generation make it more difficult for Asian women to out marry, and because they are more closely tied to their cultural groups they have less access to White males.
There are no doubt, many causes for the imbalance. Some of them have already been pointed out.
Hollywood and popular culture emphasizes the attractiveness of Asian females. The "desirable" Asian female shows up as a regular staple in movies. In contrast, Asian males are often portrayed as incompetent, asexual, or in some cases effeminate. Witness, for example, the plot of the 1996 movie "Once a Thief" (I'm remembering this from 7 years ago, so apologies if this is 100% accurate)-- this movie includes an Asian male and his adopted White male brother and adopted Asian female sister. He desires his sister, but can only have her by forcing her. The Asian female escapes her jerky adopted Asian brother and goes to the White male adopted brother who she loves. Sadly this movie was directed by John Woo, an Asian male. Similar patterns occur in other movies. In the 1995 movie The Hunted, there are two Asian women. They are both to differing levels "mistreated" by their Asian men. In one case the Asian man goes as far as to kill his lover (for some lame, whiney protoypical Asian male reason). As I recall both Asian women end up with the white guy at various times. Typically the only time an Asian male is viewed positively is when he is older and wiser and mentors a White male.
Hong Kong stars (e.g., Jackie Chan, Jet Li) have changed the situation somewhat. However, you will note that Asian men still never actually "get" White women (and rarely get any women, for that matter) in Hollywood movies (whereas the reverse White male getting Asian female is quite frequent). For example, Chow Yun-Fat appears with Mira Sorvino in the 1995 Replacement Killers. They have a pseudo-almost kind-of romantic relationship, but no, that really wouldn't happen between an Asian male and White women, so they never actually do anything and Chow Yun-Fat never gets anywhere. Similarly in Jet Li's "Kiss of the Dragon" staring Jet Li and Bridget Fonda, Jet Li never actually does anything with the girl. I understand Jet Li is in a similar situation in "Romeo Must Die". I've never seen it, I'm just repeating what I've been told, which is that Jet Li never gets to kiss Aaliyah. Comparable action movies with White male and White female stars would almost certainly have included romantic action between the leads. And if the movie included a White male actor and an Asian female, there would certainly have been romantic/sexual action as Asian females are almost always brought in for their "sexual" appeal.
Interestingly enough, other cultures have other views of Asian males. French "Art" cinema, for example, sometimes depicts Asian males as exotic sexual playthings to be used by French women (similar to how America sometimes depicts Asian females). If I recall correctly (it's been a long time since I studied these issues) the French movie Indochine (1992) provides one such example of this French view of Asian males.
The desire to out marry is in part an attempt to gain acceptance to the wider culture. To stop being one of "them" and to become part of the accepted majority. Probably if Asian females and Asian males were considered equally attractive, the out marriage rates for both would be relatively high. As it stands, since Asian females are viewed as "attractive" by society and Asian males are not, the out marriage rates stand imbalanced. Asian females are able to out marry to Whites and gain social standing; Asian males do not have that option. Some parts of the Asian culture emphasize the desirability of Asian females out marrying. For example, in Amy Tan's book "Joy Luck Club" Asian males are depicted as evil and uncaring. In contrast, White males are depicted as the true and proper mates for Asian females. For those who have seen the movie, the book is far, far worse. The book tells the story of four Chinese mothers and their four Chinese American daughters. If I recall correctly, in the book three of the four Asian daughters are dating White men. One of the three refers to a prior failed marriage with an Asian male, who she married in part to please her mother. The fourth daughter is not dating. One of the mothers who was badly mistreated by an Asian male in China is also married to a White male, who in some sense "redeems" her from the hell an Asian male put her through. The movie attempts to "rebalance" Amy Tan's original story, but does so by taking one of the jerkier of the White males and replacing him with an Asian male.
In fact, some White males actively search out Asian females. I have White male friends who go to Asian churches. Why are they going to an Asian church? The unstated reason is their desire to find an Asian female wife. There are virtually no unattached White females going to Asian churches looking for Asian male husbands. Again, a lot of this is driven by the cultural viewpoint of the Asian female as desirable (and exotic and somewhat subservient).
There are, of course, other factors as well. Physically Asian males tend to be shorter and have slimmer physiques. Culturally even some second and third generation Asian males are brought up so that they are not as "aggressive" as most White males are. The cultural values of the Asian culture are simply not as valued in our society as those of White culture. Essentially Asia has lost the culture war.
I went off on Jason because he posted a "simple" solution to what is a much more complex issue. His solution added to the stigma already associated with Asian "masculinity" and essentially repeated some of the negative statements that society already makes about what Asian men are like.
* Side note: I mentioned the African American male/White female issue. The out marriage rate for African American males is much higher than that of African American females. This has caused considerable anger in some parts of the African American population. I believe if you study Hollywood depiction of Black men and women you will discover something similar to what has happened with Asian men and women. Black men are depicted as masculine and virile. With some exceptions (Halle Berry, for one) Black women are depicted as asexual (think Oprah Winfrey, for example). The incidence of Black men appearing as attractive is much, much higher than that of Black women. Thus White women find Black men attractive, but White men are not as attracted to Black women. As with the Asian dating patterns, there are of course other factors as well, including the high incarceration rate of African American men.