Saw the thread too late!
Was going to suggest waiting till Apple cleared up the network backup issue before buying one - Time Machine doesn't work with the AirPort Extreme Base Station as yet, and network storage sharing seems flaky.
That said, I'm sure you'll enjoy the base station. It's definitely not the cheapest available, but it's easy to setup and works reliably. The printer sharing and extra gigabit ethernet ports are big pluses too!
And as for the network sharing and backup, I'm quite confident Apple will release a firmware update that will fix these things - it'll only be decent that they do so.
Arstechnica.com did a comparative review of the 802.11n base stations a while back, and I think one of the tips is to use the 5GHz channel if you can. That will boost the speeds cos it's less congested with other base stations, cordless phones etc. But that's not good if you have legacy 802.11g or b machines on the same network