Dropbox is a file sync service. You can put it on multiple computers and it will keep a particular directory (usually "My Dropbox") in sync between the computers. There's a web interface, but it's a bit clunky on the Droid (can't do file uploads for one). DroidBox is an app that works with the web interface of Dropbox. It's not perfect (it doesn't keep the directory sync'ed automatically), but it is easier to use than the web page and allows uploading of files.