Can also be done on lots of phones if they run the appropriate OS.

Chris, I can't recommend the TomTom Go highly enough. If you do plan to use it on the bike as well then wait for the Rider.

Bought the Tom Tom Go 300 last week. Very impressed so far, and have now downloaded the speed camera database onto it from the net (for free)
Navigation is very good with a 3d map following you, and you can set the distance it alerts you for the 'safety' cameras.

Matt