This is why I'm disappointed that end user open source software is in such decline right now. These kinds of "long tail" user needs will never be met by the proprietary software world. Well, this particular one might, but for every need that gets implemented, 10 more obscure needs will spring up behind it.

Dropbox is making fistfuls of money, and, like all proprietary software companies, they need to stay focused to maintain momentum.

Although it might not feel like it to most people, I think we're in still in the dark ages of software. Not quite as dark as the Microsoft era, but dark nonetheless. We just don't have the tools, infrastructure, and culture necessary for open source to really be a viable space for the typical, scattered programmer to spend their time. I'm optimistic that will change, but I'm not sure how long it will take.

It's a UI issue. Where would an arbitrary directory show up on other devices? How could you tell quickly which files on your device are being shared?

https://www.dropbox.com/help/175/en and a symlink?

Same here except the feature I am waiting for is a full featured Android client ie sync all files to the local Android device filesystem (with the option to only sync when connected to Wifi).