Was in Comet on Friday evening and I picked up a card from the TomTom stand.
The card says:
+2 Years Free Map Update Service (worth £69.95)
I tried over the weekend on my GO 730T, which I brought Sept 08. The code allowed me to upgrade to the 8.15 2GB Euro Map (upgraded from 8.10). There is a newer map (8.25) not sure why I wasn't given this update.
Anyway now when I click on the option from TT Home to add maps, the window that says "Do you want to join the Map Update Service" is no longer displayed. I'm guessing this has worked but worst case I got a free map update out of it!
Note this only works on the GO models. The Comet I went to was in Greenwich.
I've still got the card, if someone lets me know how to attach images I'll post it up.