Especially if you've got some rare, hard-to-find tracks in your library, do not rush to get rid of the lower bit rate ones and replace with the "matched" ones in bulk as Jason Snell of Macworld suggests here. Basically, I have a very rare instrumental version of one of my favorite albums, and iTunes was able to match it. Yeah, rrrright! Just to be on a safe side, I decided to replace only one of the tracks with the matched one. Guess what, it replaced it with the regular album version. I wish iTunes matching were smarter than just looking at song titles and artist names. I've got so many different versions of songs like radio, choral, live, acoustic, extended, dub, re-edits, etc, etc, etc. Just a forewarning, not a rant.