Its about time that iTunes has added this feature.
I only wish they added it a couple years ago so I could have a better idea of what songs I dont really like that much.

Skip-Count

Unfortunately according to snyder's comment on Digg it only adds it as skipped if you skip it between 1-20 seconds into the song. This kind of sucks.

There should be a better scoring system.... ahem... ;)
DigitalPimp

I still need to find a way of automatically creating playlists that are optimized to my exact mood and preferences.

This is definately a step in the right direction for iTunes though.