Here is my experience so far.
Got my iphone end of the second week, right away, was getting 1-2 mbps pretty regularly on 3G with almost no 3G reception issues. Was as happy as a little girl.

Being in a .5 Mbps wi-fi hot spot and getting 2-4 times the speed with my 3G was awfully cool.
Then after 2.0.1 that changed, started getting very inconsistant 3G reception and speeds, one second I'd get 1500K, the very next, in the same spot, 300K, it was all over the place, Id have 5 bars one second, 0-1 the next, sometimes it would switch to Edge even if I had a 3G signal. I wasn't that happy little girl anymore.
Then after seeing my 3G reception and speed all over the place for a while, along came 2.0.2, at first I didn't see improvement, then all of the sudden, I did, but, and this is totally subjective, I don't feel like it had anything to do with the update, rather it feels like the 3G in my area was worked on and improved. I'm in the Ft. Lauderdale area of FL by the way.
In any case while it is still somewhat inconsistant, overall, lately, Im pretty happy with it, usually have 3-5 bars, and even on 1-2 bars, I get decent speeds, in fact, my speed seems to have very little to do with how many bars I have and more to do with times of the day. There tend to be certain times of the day when the speeds are slower, I attribute that to limited bandwidth/lots of people using 3G.
Just did a DSLR test and got 1360K, can't complain.
I do want to say I feel very badly for those who aren't getting good 3G performance, frankly, I'd be majorly pissed as the faster 3G speed was pretty much the only reason I upgraded. Take away the good 3G, and you're left with a buggy Gen 1 that you're paying more to use.
One last thing, I was in St. Thomas this past weekend, first time Ive been in a non-3G area with my phone, so, I was left with Edge only for 4 days, it really felt like going back to dial up from DSL, it was painful. Funny how you get used to something.

I love my 3G performance lately, but have no illusions that it can't just disappear tomorrow, Ive already seen it happen, it can happen again, so, I'm enjoying it while it lasts...