Dropbox is an awesome little service, allowing you to sync various files between devices (PCs, Andriod and iPhones for example). Whilst there are lots of uses of the Dropbox service, I tend to use it for two main things.
The first is as my own personal SVN-esque server. I set up a folder in my main Dropbox “root” directory, by default in Windows this is under “My Documents/My Dropbox”. Any code I write, I save in this folder. The code is then synced to all my PCs automatically by Dropbox, allowing me to work on the code from anywhere. As I use Eclipse to write my code, I have set this folder as the default source folder for my workspace in both my Windows and Ubuntu version of Eclipse. Thus, all I need to is open up Eclipse and hit F5 to refresh and get all my updated sources, thanks to Dropbox!
I do the same for the music tracks I am working on under Renoise. By saving all my songs in a folder under the main Dropbox folder, the tracks are synced across all my accounts. As Renoise is cross-platform (to a degree) I can simply open up Renoise on both my Windows and Ubuntu machines and work on the same track. Sweet. This trick works for any cross platform program. You can do it for your Firefox or Google Chrome profiles, or even your Music Library!