The only problem I have with Dropbox is that every time someone discovers it, they feel the need to pimp everyone they've ever met with their referrer code in order to get more space. For that reason, I'm oot.
It's a shame, because as far as I can tell it's a great service, but I don't use it on principle because of the user-aggressive marketing it promotes. I've been using Live Mesh for a while, which is a similar service from Microsoft.
What I like about Mesh is that it integrates with other accounts (eg, I can have a folder on my desktop called "Andrew" and when I copy stuff to it, it appears automagically on my mate Andrew's PC at home; makes it a breeze to send stuff to each other). What I don't like about it is being MS there's a shortage of clients for non-Windows phones.