MotionX is awesome on the bike in Australia (where I'm based) - my cellphone plan has lots of data included so I never need to worry about that stuff.
I'm wondering, what happens with map downloads when I go overseas. I was thinking of getting a TravelSIM which comes with 1GB of 'data'. I'm a bit of a tech idiot with these things --- does using Motion-X GPS use up a lot of data on the phone? Or will I need to download/cache maps for offline use?