As I mentioned on Twitter a few days ago, I took the plunge and decided to give iTunes Match a try. My home library has about 12,500 tracks, and much of it has been ripped from physical CDs and stored in Apple Lossless format. My library lives in a Drobo attached to an old Mac mini with a G4 processor. Since backups and slinging music around the house aren't terribly processor intensive tasks, the mini's been able to soldier on quite nicely in this role.
Well, it took the mini about 2.5 days to match all my stored music to what's available in Apple's library. It seemed to do a good job of matching music that I'd purchased from Amazon or the iTunes store. However, it seems to have done a pretty poor job of matching the ripped tracks stored in Apple Lossless. In fact, right now my mini's trying to upload about 2/3 of my music library to Apple's iCloud.
I'm not sure that that's what Apple really intended.
Even weirder, quite a few albums didn't match all the tracks. For example, all the tracks on Amy Winehouse's "Back to Black" matched with the exception of "He Can Only Hold Her." Conversely, The Beatles' "Beatles VI" only matched two of the twenty-two tracks: "Kansas City" and "Every Little Thing."
Another thing to note is that my iOS devices were a bit confused while my mini was matching, especially while I was on the plane and had no data service. I would try to shuffle the music that was physically on the device and the shuffle would stop after a random number of songs. I say "stop," but I kind of wonder if it was just trying to play tracks that were on iCloud and timing out, slowly, on each song? I've since learned that in Settings-->Music there's an option called "Show All Music". I'm guessing that turning that off prior to hitting play would eliminate this.
With all the travel I do it's nice to be able to call on my home music library whenever I want. Assuming that all my music gets uploaded in a reasonable amount of time, I'd have to say that the service is worth the $25/year.