i was in europe (i live in uk) recently and open/closed the ovi maps application on my N900 on several occasions and didn't use a single kb of data - and i had no charges on my bill to indicate otherwise. i used no data at all on my trip.

i had turned off the assisted gps and set the roaming to 'always ask'. when opening the app it did always ask for an internet connection but i did not select one and just went into the maps. it does take longer to find your position without the A-gps (which i think does need use a data connection) though.