My review of the new AirPort Extreme Base Station is up at Macworld: This lengthy review, aided by several colleagues at the magazine, covers a lot of the basics for home users. I gave the unit 4 1/2 mice for how well it lived up both to its potential and how well it works. I was able to see consistently high speeds in testing, in excess of 90 Mbps in a single direction over 802.11n to Ethernet (flooding packets from N to Ethernet), and about 50 Mbps when flooding from N to N via the base station. My conclusion is that the device really needs gigabit Ethernet to achieve its full potential.
You'll note that the AirPort Extreme is what I was referring to in a post a few days ago in which I described how I developed new testing methodology for Wi-Fi gateways. The Extreme has a minor flaw that won't bite many people in its ability to pass traffic at full Ethernet speeds across its WAN port when network address translation (NAT) is engaged. Apple said they are looking into the problem, which is software based. A source unconnected with Apple provided convincing proof that the AirPort Extreme uses NetBSD as its embedded operating system, and that the network stack in that OS could be at fault. But it could be trivial to fix, too. (Update: Not to be obscure about NetBSD: the Acknowledgements.pdf file found on the CD-ROM that ships with the AirPort Extreme provides full copyright and acknowledgments credit for included software, as required by a host of GPL and other licenses. NetBSD is thoroughly acknowledged there; the DHCP software is credited to ISC.)
I'll be writing more soon about particular aspects of the base station, but for now, I'd like to direct you to the technical discussion about the Extreme's use of IPv6, the next-generation Internet routing protocol that's been "next generation" for something like eight or nine years now. IPv6 support is found throughout Mac OS X and is fully supported in the Extreme base station--so fully, Ars Technica's Iljitsch van Beijnum reports, that by default every Mac OS X computer that connects to a new Extreme gateway will be fully reachable through tunneled IPv6 from the rest of the Internet.