I discovered a nifty service for Mac and PC a couple months back called DropBox. It allows you to transparently sync files in a directory over multiple computers, storing files locally and online, while also providing group sharing of files with recoverable revisions. Very cool stuff, reminding me a lot of a hack for Gmail I used to use, but more refined. The above 'getting started video' is linked to their website.
The service has been in beta mode for a while now though, only accepting new members via invitation. I just happen to have a few spare invites to the service... first 3 people to email me asking for one gets an invite! punkrawker at gmail dot com