Update: Apple let us know that you can't identify systems with the Network Utility; the 802.11n capability only shows up if you've used the software update, so know your mac and get the update if you need it. Also, the $1.99 update is considered by Apple to be a site license, so you can upgrade all the machines in your home with the single $2 purchase (if you didn't alright sign up for the router). Not bad!
Update 2: It wasn't entirely clear before, but the launch of the Enabler coincides with the launch of the AirPort Extreme today, too. Don't let the "Estimated Ship: February" on their site fool you, Apple is definitely shipping now.