Has there been any headway on this issue? I have the same problem, it takes a long (LONG) time, then backs up a couple hundred kb and stops. The Time Remaining will show 146 hours (example) and the bw will fluctuate without any noticeable pattern. Stopping/restarting did not help. Sometimes, leaving the app running and returning to the home screen and then going back to the app will show an increase in bytes backed up (first time only). I assumed that this was the app updating the display and flushing the queue.
I have removed/re-added my dropbox account. There is plenty of space in my dropbox account.
HW: HTC One V, ver 0002
SW version: 1.08.652.11.710RD
OS: Android 4.0.3
HTC Sense: 4.0
HTC SDK API level: 4.21
I found SanDisk from an article on how to back up your Android devices to the cloud, on http://www.androidauthority.com