We've had pretty good luck as far as produce goes. I think 4-5 things have been bad, to various degrees. But even then, it has saved a TON of time, even if I go in and pick the things I'm particular about. I'd say 95% or more is to the quality I would pick, 4% is "passable", and 1% has been "straight into the trash". The stores have never had a problem crediting us on any mistakes.
It saves me probably an hour a week, plus there's reduced "impulse buying".