Not being an owner, but only somebody who researched the hell out of this product, people generally like the sound quality. But others complain of a hiss in the larger capacity models, and the overall volume being way too low.
jonnyboy is right. there is a definite hiss problem in my 30gb version, at least with sensitive earphones. The volume is a bit low, but the SQ isn't anything to sneeze at. The EQ definitely helps a lot.