Update: Just relinked my NAS to my dropbox account and all is now fixed though it is taking a while to reindex all my files.
As for failure symptoms - dropbox was running perfectly correctly, but it had lost authorisation to access the internet based service so was simply sitting there waiting for authorisation to be granted. I expect that the addon, post setup, does not monitor the dropbox service status - just whether the dropbox process is running or not and assumes if so that all is OK. That's probably what can be enhanced as there are command line utilities that check the actual service status - might already be used by the installer, I haven't checked
We should wait for WhoCares? to chime in - he may have already been looking at this.
I can't think of anything I may have done locally to cause my setup to requiring relinking, so I'm suspicious something has changed on the dropbox side of things
NAS: Ultra-4, NV+ & Duo v2 :: ST31500341AS & HDS723020BLA642 Drives
Network: Netgear GS108Tv2 / DM111P :: Airport Extreme / Express & Time Capsule
Clients: OS X 10.6 - 10.8 :: Ubuntu 11.x :: Win 7 + SP#1
UPS: APC ES-550