The Airport Express has received a radio upgrade. It is now an "N" device and will not be responsible for slowing down you "N" network. I'm sure there is probably a good reason, but I really wish they had done this at the same time they released the "N" speed airport extreme.
The Airport Express is a device that should not be overlooked. For $100 you can stream music to your stereo, put a printer in the closet, get the internet to a computer with no wireless, hook your xbox into the network, or increase your network signal. Obviously you can't do all these things at once but having it around sure is handy. Since Apple TV also does AirTunes, I was able to liberate mine from my stereo and now I've got it managing a printer that just does not like to play nicely off a USB hub.