This looks to my like a cynical attempt on the part of Dropbox to get users to give Dropbox permission to access all their other online accounts so that the data from those accounts can be collected together.
While it might be nice to have one login through which I could access all my online activity, I certainly don't want that login to by under the control of some third party entity (like Dropbox). If what was being talked about here was a server component I could run on MY server, under MY control -- and if I could be quite certain that it didn't "phone home" with MY data -- I might be interested.
As it is? Nah.