This may or may not be news to you, but I just found out about AS3MUL this week and I figured I 'd share in case someone out there is interested. It's a multiuser library for Flash that makes creating multiplayer games and applications pretty easy! I was able to throw together a simple test scene in just a couple of hours using this library; definitely worth a look.
Anyway, check it out if you're interested!
And if you want to see the demo scene I did, it's here