I haven't seen over 22 mbit/sec, even though I have seen up to 38mbit/sec on my desktop and notebook. (And confirmed that the Macbook can do it both wired and WiFi.)
I suspect that the WiFi speed is constrained by some hardware or software limitation. Apple's been getting better on this, as my iPhone 3G was limited to 5mbit/second, and I know the 3GS is better.
Of course, Speedtest, etc. really isn't the right way to test this. I'm a developer, and am thinking of porting iPerf to iPhone/iPad since nobody seems to have done it. iPerf is a client/server for testing throughput between any two points. So, you could install the server on some computer on your LAN, and run the client on your iPhone/iPad.
(Only thing I cam across in Google searches was some developer offering a lowball $100 on Rent-a-Coder to port it. I think the listing died.)