So gov78 and I just played some co-op in the pyramid, and it's really fun. It took us a couple tries to get the hang of it, but we eventually cleared the first boss on the fifth floor, and ended up getting wrecked by the boss on the 10th floor.
You get to keep the items that you acquire, but you don't gain any experience.
Overall though, it's a blast. It would be great to get teams of 3 going. We definitely could have used another person.
We were both around level 25, and it's going to take more leveling and better equipment to get past the 10th floor.
I hope more people can join in!
BTW, the best way to organize is probably in the IRC channel, so come on in! No one bites (much).