Using Dropbox with minimal window managers that don't have a dock/panel area, and when you don't use Nautilus as a file manager. It's pretty easy with the latest forum release, but this guide is handy for setting it up properly, including adding it as a daemon.

Nifty hint that could be extended to do fancier stuff. I must say that I think the new Dropbox iPhone client is brilliant. Being able to view and/or email a link to a document to someone while on the move will probably save my vegetarian bacon one of these days.