Apple's Airport Express became available in Europe last week, and I decided to buy one (with the aim of clearing up a bunch of sprawling cables). I was a bit apprehensive, as the reviews and specifications available were fairly vague, but it's turned out to be an excellent little box.
The Airport Express (AX) is basically a wireless router, which justifies its €150 price tag by including a 3.5mm jack for audio output and a USB socket for printing (though I have no need for that one). This means you can have your laptop anywhere in the apartment and be able to a) connect to the internet and b) play music through speakers attached to the Airport Express.
My cable modem takes the one ISP-provided IP address and assigns it to one device. Connecting the AX by ethernet cable to the modem allowed that IP address to be assigned to it using DHCP. Any computers with wifi cards (Airport or Airport Extreme on the Mac, 802.whatever on the PC) can then connect to the AX and will be assigned an IP address in the 10.0.1.x range (which can be switched to use other ranges if preferred). This is all done automatically through the Airport Express Assistant, which creates the wireless network and sets the level of security (ie the password encryption which prevents other people from connecting).
As with any router, incoming connections will be blocked, which means that protocols like BitTorrent or Soulseek don't work very well. Luckily, the AX can be configured using the Airport Admin Utility: in the Port Mapping section, enter the IP address assigned to your laptop (usually 10.0.1.2) and the ports required in both the Private Port and Public Port sections. For example, forward ports 2234 and 5534 for Soulseek, 6346 for Gnutella, whatever ports are set in donkey.ini for mldonkey and ports 6881 to 6889 for Bittorrent (Azureus only needs port 6881, in fact).
Opening up iTunes adds a new button at the bottom of the window showing the remote speakers as an output device, and playing a track sends it straight out. iTunes seems to use a bit more CPU (averaging about 15% rather than 10% before) to do this, probably due to converting the audio to Apple's Lossless Audio format for streaming; also it does make throttled work a bit harder. The main problem is that the audio output is limited to iTunes - though I'm mostly using iTunes for audio anyway lately, for its iPod integration, it's hugely annoying to have to drag the speaker wires across the room just to listen to something in a different application. This audio device has to work at a system level soon, hopefully with Tiger at the latest.
In summary, this is a well-designed, easy to use and configurable wireless router, with the bonus of wireless audio which is definitely beneficial if you listen to most of your music in iTunes.
Update: Thanks to the creator of throttled, here's a rule to add to the throttled-startup file that will allow iTunes' streamed output to bypass the firewall:
/sbin/ipfw add 00005 allow tcp from any to 10.0.1.1/24 out xmit $INTERFACE