Something I’m currently working on is a DropBox client for WP7.
It integrates with the Pictures hub, and the Music+videos hub, so you can transfer media from DropBox to your device relatively seamlessly, though I’m working on adding the Office hub as well.
I’ll also be releasing a library+source code (that gets around the fact that WP7 doesn’t support synchronous web requests for some unknown reason), so you can integrate DropBox with any application you want.
There’s a bunch of pictures below.
Any feature requests?