It's fast, f**king fast even on a 3G.
It slows down when there's lots of buildings being drawn in London (I tried by the tower of London), but even then i'd say it's about the speed of TomTom, but TomTom looks crap in comparison.
UI is a bit sucky, looks like a gash-droid application, they need to make the menus and input iPhone native.
It's fast at finding locations, TomTom crawls when selecting a destination on a 3G.
Will try it in anger later, will install on the misses 3GS as well, I expect it to fly with with the 3D eye candy.
Edit:
It's got a button on it to report police speed traps. lol