Here's the deal. You load a couple of agent programs on your PC (there are versions for Windows, Mac OS X, and Linux available). They find your music files and begin to stuff them in your locker. You can synchronize in either direction (send everything up, send everything down, or both), and specify particular folders or directories that you want it to search for the music. The service also offers a Web client, so you can listen to your tunes directly from your locker when you aren't in front of your music library.
The free version doesn't let you synch your files, but the paid version comes with unlimited storage for a year for $40, which seems reasonable to me. I tested on Mac and Windows, sending files both ways.
There are several things that I don't like about the product. First, the software agent, called Oboe, is available in two pieces: one for iTunes to synchronize playlists, and one for all other music players to synchronize the actual song files themselves. You need to run both if you want the full iTunes functionality, but I found lots of instability issues when I did: several times Oboe would go out into the ether and get lost trying to synchronize my files. If you don't care about your playlists or don't have many, then just use the regular flavor and don't worry about it.
I have a music library approaching 20GB, and it took several 24-hour days to get all the files stored in the locker. My first hurdle was that my PC went to sleep during the lengthy synch process; once I forced it to stay awake and on task, things went better. If I didn't load the special iTunes Oboe agent, I usually got better throughput.
The synch service works as advertised. After my massive upload, I ripped a few more CDs to see what would happen. They were quickly found and dispatched to cyberspace. The only issue was that the time estimates were initially way off -- in one case, I had more than 150 files that Oboe was telling me were going to take 18 hours. Ninety minutes and 30 files later, the completion time was down to six hours. My performance was about 20 files per hour when all was said and done -- but then I am connected via a cable modem operated by a bankrupt provider.
Once the files are uploaded, Locker will tell you under its "tune up" section whether your ID3 tags are incomplete and need additional editing. Its user interface is very close to that of iTunes, so using it is a breeze.
There are other products out there that can do something similar to Locker, including foldershare.com, which is now owned by Microsoft and can copy any set of files up to a spot on the Internet. Locker and Oboe come from the same people who are behind Linspire, the version of Linux formerly known as Lindows. If you need the peace of mind to store your music somewhere off site, then listen to Oboe and see how it plays with your collection.
David Strom is a freelance writer.