Where I am, I seem to get about 200KB/s (so I'd assume about 1600Kbit), which I can't really complain about given I'm in a rural-ish area. I think when I was staying in Peterborough last month, I was managing 300KB/s (approx 2400Kbit).
I believe I'm right in saying the max for 3G is 3600Kbit, and HSDPA is 7200Kbit, so assuming I was only on 3G, the 2400Kbit I achieved was 2/3 of the maximum possible, which I think is fair (much like broadband claiming 'up to 8Mbit' and actually achieving 5>6Mbit.
I gave up with 3 because where I lived, it was either 3G or nothing - that is, there wasn't any 2G coverage, and as soon as you left a 3G area the phone was useless. I also don't recall the 3G speeds being any faster than what I currently receive with O2. I'm 10x happier with O2 customer service compared to that I received from 3, which resulted in me never wanting to touch 3 again after being lied to over and over again.