An upcoming 1.08 update for Diablo III — there’s no ETA yet, but it’s available now on the pubic test servers — will recalculate the value of co-op sessions by providing an incentive to team up with other players: extra experience points! This will presumably make up for the inherent inefficiency of multiple players not being able to get their acts together. From technical designer Wyatt Cheng’s developer journal entry:
We’re still working on the details of what that buff is going to be, but at the moment we’re looking at 10% more XP per extra player in the game for a maximum bonus of 30% more XP in a 4-player game. This bonus will be multiplicative with MP bonuses. For example: suppose you are playing on MP10 with an XP bonus in Inferno of 510%. This means a monster is worth 610% of its normal XP (510% more). If you are playing in a 4-player game the monster will be worth 793% as much XP as normal. On top of this, you will also earn a flat 10% Gold Find and 10% Magic Find for each additional player in the game, and this bonus can exceed the 300% Gold Find and Magic Find caps.
Furthermore, when I’ve found something worth attacking, folks will know even though they’re back in town breaking down their blues with Haedrig.
Starting in 1.0.8, when a player deals damage to or takes damage from an Elite pack or Treasure Goblin for the first time, a notification will be sent out to the entire party to let your teammates know what you’ve found. This will be accompanied by a “combat” icon on the mini-map so other players in your group can locate those enemies. On top of that, we’re also going to put a combat icon over your banner in town. This way, players who are in town will know that you’re fighting an Elite pack or Treasure Goblin and be able to quickly determine whose banner to take to get right into the action.