Chef, I've been looking at another technology as well called Nirvanix due to scaling the site in the future. It's very safe and inexpensive for businesses now.
Here is a link but I still need more informations on the product so if you interested in reading up on it feel free... I'm not sure how much drop box is but nirvanix can already be programed as a service for a web page & share permissions with members. I just havn't had the time to research these type of products very far as of yet.
One thing is for sure " These type of compaines are going to make space hosting companies a bit upset & enable offsite backups to be maximized!!!"
Enjoy