I don't know why I hadn't been paying attention to Dropbox before. It looks pretty useful. I'm not quite sure how long it's been around, but it seems to be fairly mature, and from what I've heard it's pretty reliable.
Other than on the Dropbox site, are there good usage stories out there about people who use Dropbox, what they use it for, and what their experiences have been? I found this nice writeup, are there other similar articles I should read?