i hated that - one of the main reasons I don't use dropbox. Early on I had a bunch of clients all raving about how cool dropbox was - each sharing 200-500meg projects with me. Within days I'm hitting a 2gig limit, being encouraged to upgrade my account just to use a service someone else was forcing me to use. I use DB as little as possible.

Agreed, although it starts getting complicated if you put stuff in there too (do file creators pay? shared folders pay? what if that owner wants to drop out, can they re-elect someone else)? Anything but this method starts to get really complicated.

It's not that complicated. Have the user toggle an "I also claim ownership of this directory" flag before letting them edit it and have it count against their storage after that.

(No idea how difficult it would be to introduce this into their system, but conceptually it's a pretty easily surmounted problem.)