Apple has quietly released iTunes 10.5.1 to the public, which enables support for its iTunes Match service. The service allows syncing your music library to iCloud for easy remote access from other computers or iOS devices. But don't get too excited just yet, as iTunes Match's hard 25,000 track limit means those with extensive collections simply cannot take advantage of the service.

iTunes Match is a subscription-based iTunes library syncing service that works with iCloud. Unlike Amazon Cloud Player or Google Music services, iTunes Match can identify tracks in your library that are already part of the iTunes Store's extensive library of music. Those tracks are immediately added to a user's iTunes Match account by connecting to the 256kbps, DRM-free version on Apple's servers. This is true even if you ripped the album yourself at lower bitrates using older versions of iTunes or other software.

The remaining tracks, up to 25,000 total, are then uploaded to iCloud. Any songs purchased directly from iTunes don't count toward this limit, but if you have more than 25,000 tracks not purchased from iTunes in your library, the service simply refuses to let you sign up. Apple has yet to make any allowance for users with massive libraries to choose a subset of their music to upload—an unfortunate limitation in our view, since such avid listeners are among the most likely to consider paying the yearly $24.99 fee.

On the upside, iTunes Match also syncs all of your playlists across devices. Once your library is uploaded and synced with iCloud, you can turn on iTunes Match on an iOS device and access individual tracks, whole albums, all songs by a particular artist, or any of your playlists. Clicking the small iCloud icon downloads the files and adds them to the library on a particular device, while selecting an individual track appears to merely temporarily cache the file long enough for playback.

Apple missed the planned end of October launch for iTunes Match by a couple weeks, re-releasing iTunes 10.5.1 betas for testing by registered developers over the last month and a half. At the time of publication, the final version of iTunes 10.5.1 was not available from Software Update, but it is available as a direct download from itunes.com.

UPDATE: Fortune reports that iTunes Match is already oversubscribed, with Apple's servers unable to activate new users. Apple is recommending trying again in an hour or two, though we, like Fortune, recommend maybe waiting longer if you're not in any hurry.