1) Yes, and it should remain so. No.
2) Eh. 5%? Who cares. I don't know.
3) Yes, there are. Doesn't exist yet, and when it does it's going to work on XP also.
Only downside to 64 bit that I've found is that the Cisco VPN client doesn't work. That's the case with 64 bit XP also, though. I have been a fan of Vista since the first time installed it. I haven't experienced any real problems with it, and it looks nice. It has a few things going for it that XP doesn't, and for me doesn't have any real downside (I have MSDN, so it's free).