Played around a bit more with synchronising music files to my iPod (now on OS 4.0.2). I have started using the iTunes installed on my new Desktop PC (Dual boot Win7/Ubuntu10.04), so at least iTunes works a bit better (but for a product from a company that claims excellence in user interfaces, I do think it rather poor). Anyway, the upshot seems to be that Rhythmbox can play music files from the iPod, can copy music files over to the iPod, but not update the database properly - hopefully new packages will soon be available to cope with this). So the end result of all my efforts was to clog up the storage on the iPod with invisible (to the iPod, anyway) music files. I set the iPod up to rscrub and reload music, which took several hours, into the early hours of the morning.
So, to continue with the military metaphors of recent posts, this ongoing skirmish still seeks resolution.