I did not allow Zune to do this, the first time I installed the software, last year. It basically fucked up about 80% of my tags and inserted totally wrong album art for a good number of my albums. I'm still fixing that *sigh* The problem here is I have some albums that are on the marketplace and have artist data like pics and stuff, they're not coming up because the album I tagged is tagged slightly different. But, the flip side to this is letting Zune scan and tag everything and me being left with a clusterfuck of wrong tags. Dunno why it happened the first time because my tags were uniform and 100% correct. But it made a huge mess of my music.
As for the rating, I like to be able to say I really love a song, or I somewhat like it. I'm not as simple as "I like it" or "I don't like it" In iTunes I have every song rated. A lot of days I'll sync a playlist that's 3 stars only because I'm always listening to my favorite songs (4-5 stars) but change can be nice. I don't have any music in my library I don't like, so a broken heart is very pointless. At worst I have some songs that aren't my favorite but I still like time to time. Those are the ones I rate 3 stars.