This morning I upgraded my laptop from Ubuntu 7.10 to Ubuntu 8.04. The whole process took almost exactly 4 hours. The only significant problem was that sound was no longer working properly from within Firefox. BBC Radio was silent on the BBC iPlayer, and when I selected to play it in RealPlayer, I got only garbled speech. However, I could listen to it by starting RealPlayer10 outside Firefox and manually entering the URL of the .ram file.
A quick search on Google revealed a post on Ubuntu Forums that suggested it might be a problem with the Totem plugin, and that the MPlayer plugin might be better. I started Synaptic package manager and completely removed the totem-mozilla package and installed mozilla-mplayer instead. Now both the BBC iPlayer and RealPlayer work from within Firefox!