It's definately less than brilliant on the 3G, it's ok if you're standing in a field somewhere, but try driving through the centre of london and you soon start finding yourself "apparently" on a different road to the one you're actually on. I've not had any of those problems since I got the TomTom cradle, so for the 3G it's a definate improvement (and necessity) in a urban environment while driving about.

The 3GS is supposed to have improved GPS reception, although I've not really tried it out, suppose I could get my fiance to sit in the car holding both phones (she has a 3GS) while we go for a drive and compare the TomTom results.