Also hidden away in the Airport Extreme revision are software enablers, included with the base station, to field-upgrade the wireless cards in some currently-shipping Macs to support 802.11n, no hardware changes necessary -- we suspected that something like this was in the works. Per Apple's 802.11 page:
These Mac computers support 802.11n in the new AirPort Extreme Base Station using the included enabler software:
- iMac with Intel Core 2 Duo (except 17-inch, 1.83GHz iMac)
- MacBook with Intel Core 2 Duo
- MacBook Pro with Intel Core 2 Duo
- Mac Pro with AirPort Extreme card option
Thanks Jeff L. and everyone who sent this in.