When that ad aired here, it was saying "What is 3g?, it is what helps you download twice as fast", implying performance of downloading and such was twice as fast as edge. And thats true as a baseline, and to me pretty honest of what to expect. I wonder why they changed the wording in the UK to make the ad seem to be hinting at the real speed being what they were showing.
http://www.youtube.com/watch?v=aPWBmAJQ1tITheir newest ads also do say "sequence shortened" when showing the phone functions.
Of course
next to most other phones, the iPhone does appear really fast.