A quick note – I’ve been having problems with dropbox not working on my Ubuntu systems. It would try to re-install the software every time I restarted the system, get to around 97% unpacked, and then hang.
I eventually figured out that the problem was the mount flags for /home. For security reasons that partition is mounted nodev,noexec,nosuid but the dropbox script is loaded in my home directory so I need to remove the noexec flag. Now it loads properly.