"iRATE makes you become critical of music. I've noticed myself wanting to click on "This sux" a few times while listening to broadcast radio. Others have been known to want to click "This sux" when listening to a CD."
I know exactly this feelng. Post-iTunes, I want to rate everything. I sometimes go to Amazon to just generally rate my purchases "to improve my recommendations", even though I rarely pay any attention to the recommendations (Tom and I had a recent chat about Amazon recommendations, both concluding that they were generally rubbish, but at zero cost (now it's been developed) they might as well leave them there - they probably click-thru just enough to justify the screen real-estate. No more.) Anyway, I rate the purchases just because ... I like rating. It's even more of an addiction with my own music (yet another reason to get a new iPod - ratings on the move.)
iRATE looks kinda interesting (though has a terrible icon on MacOSX!). Here's an interview with the creator, at Kuroshin.
And here's iRATE itself.