If you can make it so that I can pickpocket weapons off high-level monsters (and my combat skills suck, but I have high level pickpocketing), then that would be fun.
It provides an alternative to becoming a fighter-type, and instead concentrates on stealth and stealing.
Of course, it would be nice to have \"thieving\" skills to complement cooperative play too... Like in EQ, the rogues can drag corpses so clerics can revive them.
Other thieving skills that I like to see is lockpicking skills... perhaps to free people from prisons, or just to open an important room in some dungeon without looking for the key... Maybe if some dungeons contain a lot of locked loot rooms, people would be more inclined to hire thieves in a party.