Will report back on success/failure.
UPDATE: The next day...
Worked pretty much fine. Had to do at least one extra upgrade after it had finished to get everything updated, however this was shown by the automatic updater tool so normal users shouldn't have a major problem.
Firefox 2 is nice. Now uses the standard icon (Ubuntu decided they could live with that unlike Debian?). Movies work out of the box so can browse Apple.com trailers etc. It has crashed once on me so far (but new crash catcher seems nice). Hopefully Edgy will pick up the flash 9 plugin when it is formally released.
Startup screens etc seem more colourful and cleaner - a bonus for Joe User. The startup actually seemed slower, but that could just be because there is no boot text now. I must check if escape shows it as it can be very useful.
Aside from that haven't noticed any stand-out changes. I guess it's mostly just polish. I must try Rhythmbox/Banshee - I think they'll support my iPod now. Things like F-spot are formally supported (it uses Mono) so might start using that more.
Just realised that 3D acceleration is not working. But I think it's this bug and it currently marked as "High importance, fix released" so might be solved soon. Basically when I try and load the DRM module I get:
FATAL: Error inserting drm (/lib/modules/2.6.17-10-386/kernel/drivers/char/drm/drm.ko): Cannot allocate memory