Apple's AirTunes vision sounds good -- on the web page:
Apple - AirPort ExpressAhem. Ok, now back to reality. iTunes will stream to one AirPort Express Base Station (AExpBS). So you might have 3 of 'em attached to powered speakers, but only one will play at a time. So much for music throughout the house!
AirTunes Unleashes Your Music
... AirPort Express with AirTunes brings your iTunes music in your Mac or PC into your living room — or wherever in your home you have a stereo or a set of powered speakers.(1) All you have to do is connect your sound system to the audio port on the AirPort Express Base Station using an audio cable (included in the optional AirPort Express Stereo Connection Kit) and AirTunes lets you play your iTunes music through your stereo or powered speakers — wirelessly. iTunes automatically detects the connection of your remote speakers, so you just have to select them in the popup list that appears at the bottom of the iTunes window and click play.(2)
Enjoy your playlists, set iTunes to shuffle through your entire library or repeat your favorite songs over and over again — however you like to enjoy your music on iTunes, you can now enjoy it that way through your stereo speakers, wherever they’re located in your house.
Buy more than one AirPort Express Base Station and connect one to every stereo or set of powered speakers in your house — one to your stereo in your living room and another to a pair of powered speakers in your kitchen, for example. Its small size and affordability make it perfect for having more than one. Imagine being able to play your iTunes music on whichever speakers in your house you prefer.
In any case, it doesn't work all that well. Even when I stream to the AExpBS from a powerful server I get occasional pauses in the music (even with a large buffer set in iTunes -- I think the problem is that the AExpBS needs a much larger internal buffer - but see below, later I fixed this). The biggest problem, however, is the lack of remote control for iTunes (see below for workarounds).
The situation Apple ought to be encouraging is a media server holding music and Apple devices controlling that. For example, music on a G5 iMac, control via an iBook. One LAN with multiple Apple wireless devices. Well, that's what I tried:
- G5 iMac with iTunes running in a Tiger login session, connected to AirPort Extreme Base station by 10 Mbps wired ethernet. iTunes is sharing Library.
- AirPort Extreme base station configured for 802.11 b networking.
- AirPort Express Base Station attached in bridge mode to the wireless LAN, with speakers.
- G3 iBook with 10.3.9 connected via 802.11b to WLAN, with iTunes running locally. iBook streams to the AirPort Express Base Station.
- Well, the above seemed pretty obvious to me, but when I wrote it down it occurred to me that very few people are going to be geeky enough to configure this.
- The fundamental setup is stupid. The iBook isn't acting as a remote, it's actually streaming the music. Way too much work for something that runs on a battery. The iBook should be controlling the application running on the iMac. 
- There were (initially) glitches and pauses in the music. Their are multiple bottlenecks in the situation I could improve (switch my ancient 10Mbps hub for a 10/100), but I
suspect the G3 iBook is a key problem -- especially since I use WPA on my LAN. The G3 just doesn't have the firepower to do all the encryption and streaming -- especially since it's running multiple simultaneous users.  Actually, the problem persisted even after I eliminated the G3. The Airport Express really needs a large internal cache; which, of course, would make it impossible to synchronize output between multiple base stations (sometimes analog is just better!). Additionally, I've been told that the Airport Express requires an uncompressed audio stream -- this vastly increases the burden on even a perfect network. In reality, there are a lot of moving parts on a wireless LAN with two interacting base stations, not to mention my neighbors' WLANs.
 There's a neat 3rd party AppleScript application that does something like this, but it doesn't support use of remote speakers! Also, it's very early in development. This needs to be an Apple product. I also tried using 'Chicken of the VNC' to connect to the iMac's embedded Apple Remote Desktop Client, but 'Chicken' blew up. Might not have liked the large display area.
 Ok, so this is cruel. Bottom line though is that the media server should be streaming, the iBook should be a remote. Apple needs to provide the thin client solution I've been whining about for years.
- Microsoft Remote Desktop Connection didn't work as well as I'd expected! It was fine when I used it with a new invocation of iTunes, but I couldn't reconnect to a running version.
- I went looking for TuneConnect so I could ask the author about enabling control of remote speakers. That, however, led me to NetTunes. This $20 shareware app seems more like what I need -- remote control of iTunes. So see my NetTunes review. [I registered NetTunes -- but it turned out to be incompatible with both Fast User Switching and with my OS X photo images screen saver. So it bit the dust too.]
- This stuff is really not ready. The Jobs reality distortion field has been working overtime when it comes to AirTunes.
- Savvy users, I'm told, are using Mac minis as headless media servers, with remote control via NetTunes. iTunes is quite happy to work with a shortcut in place of the standard iTunes data folder, so one can in theory have iTunes on the mini and iTunes elsewhere manipulate the same data set. God knows what happens if both try to edit the db ath the same time!
- Slimdevices Squeezebox2 is looking better all the time. I'd need eed to get rid of that pesky DRM of course. Why can't Apple manage something like this? They have a very interesting discussion on the impact of streaming audio on wireless LANs:
What kind of impact will Squeezebox2 have on my wireless network?
While streaming music, Squeezebox2 will use some network bandwidth. The amount of bandwidth depends on the bitrate of the audio file. MP3 files use up to 320k bits per second, AIFF, WAV, AAC and other formats may use up to 1.5M bits per second, but since Squeezebox2 supports FLAC, this can be reduced to around 800k bits per second on the fly. A solid 802.11g network can generally support around 15-20M bits per second of data, even though it's rated for 54M bits per second. This means that you can support more than one Squeezebox2 on an 802.11g network, but the number depends on the audio data rate and how busy the network is otherwise.
- Things are looking better. My network reconfiguration (moved iTunes files off server to iMac, switched to 802.11b/locked, reset to default channel configuration) seems to have eliminated the skipping problem. Esoterica though, most won't have a chance with this.
- NetTunes often works even with Fast User switching. It's not supposed to and it's very fragile, but if I connect, make my changes, don't cause any windows to open, and disconnect I can sometimes escape alive. In fact since it's incompatible with my screen saver, it works better this way. NetTunes is really for remote control of a headless Mac Mini.
- TuneConnect is back up front again. It can't control speaker selection, so I have to remember to leave iTunes directing output to the Airport speakers - but otherwise it's a decent little remote. It DOES work fine with fast user switching on the media server, I've even had several clients connected simultaneously. Main annoyance is that it's designed to work with a string matched set of tunes -- not a playlist. Sigh. I'm hoping the developer will fix this.
TuneConnect failed. Fast User Switching breaks remote AppleScript. Now I'm trying PatioTunes. It does look like the web server method is the only one that really works. I do love embedded web servers.
I ultimately gave up around 5/06. Now the iPhone has an iTunes remote control app ....