My favourite cloud syncing app Dropbox has a nifty LAN syncing feature, which detects when two computers are on the same local network and transfers files directly between them, instead of taking the scenic route via your internet connection.
Unfortunately, this does not always seem to work. In my home setup, I have my Windows 7 box connected to the router via ethernet, while my Ubuntu 11.04 laptop connects via wifi. In this setting, LAN syncing did not seem to work. I "fixed" this problem by connecting my laptop via ethernet and deactivating wifi. Clearly not ideal, but at least I can sync my 2.5gig Dropbox folder without downloading my files at 0.1kb/sec from the Dropbox servers.