My wife got a new MacBook a few weeks ago and was complaining of slow 802.11g wireless speeds at home. Normal troubleshooting went nowhere. Configuring the access point a little differently improved the situation.
My wife took the MacBook into an Apple store and diagnostics were run on it showing no connection or performance issues. At home, it was still slow. This was odd because I have a slightly older MacBook and an even older Linux laptop working fine on the same wireless network.I searched the Interwebs and found a post on an Apple related forum, forget where now, that suggested Macs liked Channel 11 on 802.11g networks.
With nothing to lose, I logged into the LinkSys access point and changed it to listen on Channel 11 (2.462 Ghz) by default. After this change, the new MacBook wireless performance was much better. I have no idea if there is some affinity for Channel 11 in Apple's hardware or software stack, or if there is less interference on that frequency, or if there is some other explanation. In any case, I thought it was worth sharing.