Everyone who seems really excited for this, let me just say that after signing up during the developer beta, it ended up being more of a hassle than helping.
First of all, it only matched about 600 of my 2500 songs. Some of those matches we're to the wrong version of a song. I was excited for all my music to get upgraded to a higher quality, but it barely matched any tracks that I hadn't already bought on iTunes.
Secondly, songs that I bought on iTunes years and years ago and have since deleted we're all of a sudden back in my library, and there's no way to hide them.
Third, there's no more controlling what and what does not get synced to your iPhone. I have lots of music sitting on my computer that I don't want on my iPhone. With iTunes match you're forced to see every song on your phone.
Long story short after seeing what it was like I immediately turned it off. I prefer having control over my library, iTunes Match basically turns it all over to Apple.