Now that iTunes Match is live (albeit in beta form) the question will surely be asked:
I'd love to use iTunes Match, but my iTunes library has more than 25,000 tracks. When I attempt to use the service I'm told that I have too many tracks. Is there any way around this?
There is, but it's not an entirely scenic route. iTunes Match--at least up to this point--places a hard limit on iTunes libraries. Either you have fewer than 25,000 tracks (not purchased from the iTunes Store, as purchased tracks are not counted against this limit) and everything's hunky dory, or you have more than 25,000 tracks and you're barred from the door.
In a perfect world, rather than giving you the boot, iTunes would then offer a suggestion along the lines of "Since your entire iTunes library is too expansive for iTunes Match, would you like to upload some of your favorite playlists?" But it doesn't. So you must take matters into your own hands. And that means feeding iTunes Match a different library.
To do that, quit iTunes, hold down the Option key, and launch iTunes. You'll be prompted to create a new library or choose a different library. Choose the option to create a new library. iTunes will open and you'll have nary a tune in your library.
Move to the Store menu and choose Turn on iTunes Match. You'll be prompted for your Apple ID and password. Enter them and click OK and iTunes will switch on iTunes Match. Now open iTunes' preferences, click the Advanced preference, and uncheck the Copy Files to iTunes Media Folder When Adding to Library option and click OK. This will prevent iTunes from generating duplicates when you follow the next step.
That next step is to choose File -> Add to Library and browse for tracks that you want added to iTunes Match. When you're finished, choose Store -> Update iTunes Match. The iTunes Match entry will appear in iTunes' Source list under the Store heading and Match will run through its three-step program--gather information about your library, match your now-smaller library with tracks on the iTunes Store, and upload artwork and remaining songs (if the Store doesn't have some of the tracks you're matching).
Kludgy, yes. Inconvenient, certainly. But it does provide a way to make your favorite tracks available to iTunes Match. Once you do this, you can then switch back to your regular library by quitting iTunes, relaunching it with the Option key held down, and then choosing your old library. The tracks you've matched will still be available to other computers and iOS devices.
Updated to include information about not duplicating tracks.