They trade various items. The most commonly requested ones are the Feign Attack Expression Book, the Chicken Suit, Legendary Weapons in general, Pub Games items (particuñarly the high Roller's Coat) and many other things!
You trade by highlighting(sp?) the little orbs with gamerpics, that represent players, and then choosing the "gift" option, if the trade went well, your game should save.
Chicken Suit is relatively rare, so perhaps you could get some rare items or gold out it.
Any questions or doubts?
I don't give a crap.