My personal favorite apps that use the API:
plaintext: http://itunes.apple.com/us/app/plaintext-dropbox-text-editin...
plaintext: http://itunes.apple.com/us/app/plaintext-dropbox-text-editin...
Here's a screenshot of how to integrate HelloFax with Dropbox https://img.skitch.com/20111021-b2qqr3rbh5uew4jxh4c4n83pe7.j...
Hope that helps!
Just wanted to say thanks, awesome job, and I think you converted her into a Hellofax customer for life.