I love 'em. Used guns usually represent a better deal than new since someone else has taken the initial hit for depreciation. It takes a few thousand rounds for the action to smooth out anyway and very few guns are shot enough to wear them out. A visual inspection will quickly sort those out. I have ended up with a few dogs but the vast majority have been great.
I especially like brand name guns with excellent reputations that have been neglected or abused. My LGS takes guns on trade and doesn't clean them up. They just slap a low price on them and try to move them quickly. I can clean them up, enjoy them and usually break even (or better) when I sell them. Another sweet spot is guns that are slightly obscure or unpopular for the wrong reasons.
I recently bought a S&W 457 and it is awesome. It's a "value line" gun so it doesn't have the panache of a higher end model and it's only a S&W. It's not hi-cap, super small, light or anything else. It is very accurate, reliable, 7+1, .45 with an external safety. Ruger P series guns are another great example. They are accurate, reliable and ugly as sin. That makes them a true bargain.