Update: I have a better link with more info now.
My night is blown. I just got an invite to SmallWorlds, a massive multiplayer game (really world) that was built entirely in Flex/Flash by the team at Outsmart. It's an immersive cartoon world filled with Web 2.0 goodness everywhere you look. You start as with any other world by setting up your character. There are a lot of customizations you can make to your character so you shouldn't have any trouble creating a unique identity. The final customization is creating your dance; a series of keyframes where you can customize your moves. Once you've got your groove set, it's time to jump in.
You get to choose a space which is just a room that you can customize the look and feel of. There are a number of stores in the world and clicking on any item in a store gives you information about it and lets you buy it. You can buy a TV that connects to YouTube, a boombox that will play Last.fm channels and various picture frames that you can fill with Flickr photos. You can also buy games so things like a pool table that you play and arcade stand that you can play in game. Once you trick out your house you can go check out other people's stuff. A lot of the world is social so things like watching TV can be done with friends and one person even controls the remote (sets the YouTube channel).
Outsmart played with the idea of 3D Flex technology for a while before turning it into SmallWorlds. What's fun about it for me is that it's so low maintenance. Second Life always seemed kind of intense to me and SmallWorlds is more down to earth and fun. At this beta stage it's also a lot smaller so it's easy to jump in and find something interesting very quickly. I always felt like I wandered around too much in SecondLife. The familiar tie-ins with my Web 2.0 accounts made SmallWorlds fun and accessible very quickly. I think this is a keeper. There are definitely some rough spots and it takes a while to load certain areas, but all in all it's a good time.
It's in private beta right now and is using Amazon's web services. If you'd like an invite, drop me a comment or send me an email at firstname.lastname@example.org.