According to people who’ve installed Windows Vista on their new Core 2 Duo iMacs, the Microsoft OS identifies the wireless card as a Broadcom 802.11n Network Adapter. If that’s true, it means Apple’s shipping pre-N gear without enabling it in OS X, something probably coming in the future via an update.
There’s also been speculation that the Apple iTV set-top-box is also going to use 802.11n in order to keep the video flowing smoothly and not run into bandwidth issues that 802.11g/b would have. So why isn’t Apple enabling 802.11n on OS X yet? Probably because they don’t want all the tech support nightmares that a draft wireless would cause.
802.11n Wifi Card in New iMacs? [Mac Rumors]