I can't stand them and they're all over the place.
I think my biggest pet peeve of all is that they make the background music so loud you can't hear them play. Maybe it's on purpose because you can't tell they're playing it wrong (or not playing at all...)
I don't like the low quality, but hey, it's a free site, so I don't expect people to have really high quality recording set ups.
And then of course, a lot of people just don't play the song right.
One thing I don't get is guitar players thinking it's better to use the right fingering than to play the right notes...where's the logic in that?