a linux port is doable (mac will come first) -- everything's written in python and was designed from the outset to be portable. although this isn't the initial focus of dropbox, a linux port would be interesting for maintaining small web sites or web apps -- instead of using scp/sftp or equivalent you could just modify the files on your desktop and have them synced to your web host.
Congrats on a great product. A linux port would be great for servers - I'm always rsyncing stuff between my linux boxes.
For those who don't have shell access though, it would be cool if you integrated the service with (S)FTP. I don't even think you'd need to sync to the server.
Just giving the user the ability push his/her dropbox public folder to a server using (S)FTP would give your software several new use cases.
The app looks great.