Online sync'n'store services
Your files on the cloud to access from... anywhere
I’d suggest that most folk simply looking for a cloud-based 'drive' on which to hold the contents of their computer(s) in case of emergency will get a better deal from services such as Carbonite and Mozy that offer flat-rate subscription plans and dedicated back-up apps. Of the two, Carbonite has the edge. It's easier to use, and you can view your files on a broader array of devices.
Apple's MobileMe has iDisk, and if you're subscribing to MobileMe for file syncing, you can use free software to back up key files, but not your whole machine - you don't get enough online storage for that.
If you just need to dump a bunch of files online, you'll appreciate the 25GB of free storage provided by SkyDrive, and its LiveMesh add-on provides machine-to-cloud-to-machine syncing - handy if you want to access your files when you're not connected to the internet.
But, despite its higher cost and lower bundle of free storage - though you can increase this a little by recommending the service to friends, if they subsequently sign up - Dropbox remains the easiest to use and best multi-device file syncing system.
Cloud storage is here to stay, and since so much of it is free there’s no reason why you can’t try out one or more of them in order to see which one suits your needs best. After all, all you have to lose is that unsightly bulge in your trousers… ®