Pretty neat service indeed. I use it to share files with podcasting folks. They have a dropbox account, I have one, I create a directory in my Dropbox dir on my local HD, right-click on it, pick "Sharing Options" and send out an invitation to the person I wish to collaborate with. That person can then place files there. The dropbox application syncs your local files with the online space, and back to anyone with whom I've shared that folder(also Dropbox account holders). Excellent for collaboration.