Dropbox has been around for a while, but I hadn't really been interested in it until my fiancee's laptop started making strange noises. As a result she's using my desktop to do some of her work, as well as her (possibly dying) laptop. Not to mention she's constantly emailing herself files to access them on school computers. So, a backup and sync solution seems to be in order.
Having set Dropbox up for both of us, I'm really impressed so far, especially since it works seamlessly with Linux, my platform of choice. Ars Technica has a good review of the service, and many others have jotted down their thoughts, so I'm not going to go any further than saying I like it.
If you're interested in using Dropbox, use this referral link: https://www.dropbox.com/referrals/NTMyMDkwNDc5, and we'll both get an extra 250 MB of storage!