Hi.
I'm not sure that this topic title is best possible? I've been happily mining with my HD 5850 (~280Mhash/s) and recently it's become really inefficient and produces 1BTC/~144hour.. With that "speed" i can't pay electric used in mining.
there's something weird. you should be getting almost twice that. 280 Mhash/s at current difficulty should yield 1 BTC/75 hours.