I play limit cash games for tiny amounts - the amounts where people will go in with pretty much anything! - and have gradually increased my bankroll, but not by much, and am in the middle of a 50BB downswing at the moment. I use the player points this generates to buy into tournaments, though, which has more than balanced this out, so I guess it"s technically a profit.
Overall my STT/MTT performance is miles better, but I still play cash games to get a different perspective on things, and, even when losing, I think it adds depth to your game.