For just $25 per year, Apple's iTunes Match service lets users access their music library from the cloud--without having to upload every single song. iTunes Match "matches" a user's songs to master copies in the cloud, and only uploads songs that it doesn't already have a copy of. But before you dive in, there are a few caveats to consider.
iTunes Match is different from Amazon's, Google's, and other cloud music services, because it doesn't require users to upload all of their music. Instead, iTunes Match makes the user's library available through iTunes as DRM-free, 256Kbps AAC files, regardless of where the songs originally came from. The only songs that get uploaded are songs that iTunes doesn't already have. As you can imagine, this is ideal for someone who has a huge music library and who doesn't want to spend hours uploading said library to the cloud.
Apple's iCloud service backs up users' purchased iTunes songs for free, so iTunes Match only makes sense for people who have acquired their music from outside of Apple's ecosystem--legitimately or, ahem, otherwise.
But though iTunes Match debuted Monday, it's not quite ready for primetime.
First, the matching process takes a long time--especially right now, as there is a rush of new users putting a strain on Apple's servers. My 15GB library, most of which comes from ripped CDs, took about an hour to match. Uploading unmatched songs takes much longer--after a half-hour of uploading, I was only through about 20 percent of my 1100 upload items.
The bigger issue, however, is how iOS devices manage your newly matched library. Activating iTunes Match on an iPhone, iPad, or iPod Touch erases all of your locally-stored music (so it's a bad idea to turn on the service if you're about to hop on a long flight).
(UPDATE: According to Macworld, iTunes Match does not delete your local music library right away, despite Apple's warnings. To double check, I tried this on my iPhone and found that all my local music was available even after disconnecting Wi-Fi. On the iPad, however, roughly half of my library is unavailable when Wi-Fi is turned off, because the songs haven't finished re-downloading through iTunes Match. I'm not sure why my two devices behaved differently, but I'd warn against switching on iTunes Match until you have enough time to deal with any snafus.)
Songs are downloaded to your device automatically as you play them, and you can download entire playlists or individual albums with one tap, but there's no "Download All" button for grabbing your entire library. The workaround, of course, is to create a playlist that consists of your entire library, but I wish Apple had come up with a better solution, including a way to keep locally-stored files on the device until they've been replaced by their iTunes copies.
Furthermore, once you've downloaded songs to an iOS device, deleting them can be a hassle. You can either swipe over individual tracks to remove them, or you can delete entire albums by pressing and holding on them, then hitting the "X."
Neither solution is obvious, and if you try latter method on a playlist, it'll delete the track list itself, not just the downloads within them. Apple needs to make bulk song management clearer and easier for users who want to swap playlists in and out.
Apple was two weeks behind its own schedule in delivering iTunes Match, presumably because they were still ironing out some kinks. Maybe they should have waited a little longer. The service is supposed to take the hassle out of transferring files onto multiple devices, but at the moment it only causes bigger headaches thanks to long set-up times and clumsy song management.
Updated at 4:15 p.m. PT with new information on deleting songs.