I have the latest Apple Airport base station. I just updated to the latest firmware that was released.
There are times the phones are real slow downloading apps or playing youtube videos (stalling).
I have tested using speedtest, FCC, and various web based test sites. My ipad2 always has speeds above 10 megs. The iphones usually stay about 1-3 megs.
I tried testing with just one device connected but still was only able to get about 2 megs.
I have Apple TV and it downloads really fast. I have my LCD TV that has youtube and Netflix and it also works great. My son has his Android phone and he gets 10+ megs. My daughter uses her ipod touch and also gets real fast speed...It's just the iphones that seem to have the slow connection.