I knew my Macbook was supported "Draft 2" of the 80211.n standard, so when I saw a reasonably priced 80211.n router, I went for it. "It" was a Netgear WNR2000. It installed very easily. I was able to re-use my old SSID and security settings, so that I did not to change any of my devices (two laptops and a Wii) or devices of friends and family who had previously used my network. Very nice. All of my devices accessed the new network with no problem. Happy happy joy joy! Not so fast.
Everything worked great except for my Macbook. It had no problems with the network, but its Internet connection was horrible. It was like being on dial-up, and it was only this way for my Macbook. My wife's laptop was blazing along as was our desktop computer (with a wired connection to the WNR2000.) It was only my Macbook that was badwidth impaired.
I started tweaking with the WNR2000's settings, well actually just one (wireless) setting: maximum network speed. This was set to 300 mpbs, or half the theoretical maximum for 80211.n and nearly six times as fast as my old DI-624's 80211.g network. I started tweaking it down, but to no effect. Until I set to 54 mpbs, i.e. the same speed as you get with 80211.g. Then my Internet connection on my Macbook was as fast as it was for every device on the network. Order had been restored, but it is not a satisfying solution.
My only guess is that I fell victim to some kind of "mixed" network issue, but that is mostly a guess. I thought the 80211.n would come in handy when copying files between my desktop computer and my Macbook. I do this a lot for music, photos, and videos. Now I basically have the same wireless network speed as before, but I could have gotten that with a cheaper router.