The linux client for Dropbox is now available.
To put it simply - you run a client on your computers, and it syncs a ~/Dropbox directory with the Dropbox web service (which uses Amazon's S3 as their backend). You now have all the stuff you cared about synced with your desktop, your laptop, etc. As a bonus you can share directories with friends AND the web interface has built in per-file rollback version control. It's pretty hot. More info here. I use it for my wallpapers, documents, and even some dotfiles that I want on all my PCs.
Anyway this is a godsend if you have multiple PCs and whatnot, and it's the only tool in this space that I've seen so far that even tries to support Linux, and it's the simplest of its kind I've seen so far, so I give it a thumbs up.
Download here. (Note, you need an invite, and I am out, but I've given a bunch out yesterday and today to a bunch of Ubuntu people on identi.ca, so either ask around or check out their forums or something - and yes, only the nautilus plugin is GPL, the client and server are closed; so before you lecture at me go fix iFolder first plskthx.)