I just installed WPB2D 1.1 on 2 sites, authorised them with my Dropbox account, started a backup on each, and left them to it. I checked back a few times and saw the "files processed" count going up, and then a while later when I looked the count appeared to have stalled (although the timer was still moving).
When I clicked Backup Settings to get a look at the log, I was presented with the Authorise button again - this happened on both sites.
Did I somehow lose the OAuth token by setting up on 2 concurrent sites? Ideally I'd like to use it to backup 4 sites.