Oh and something i only realised when playing my 2nd co-op game a while back btw, is that there is no loot or gold sharing problem, they made sure no "ninja looters" by providing each player with individual gold and item drops, ie. u don't see same drops as other peeps, u just see your own gold and item drops, and they see different ones just for them.
But if something drops that u think will be a good item for someone in your group, you can still give items to others once u have picked em up.
Aye it tales a certain friction out of the game would even make *gasp shock horror* Public game possible.
If you send me your battle.net passwords i'll set you up a private game