This might be of some amusement: www.scenecaster.com. It's a shared 3D space generator that comes with a Voki avatar. You can design a space, currently an indoor space, and put premade things like bookshelves and playground equipment in it.
The avatar is one of the disembodied head style. I started doing what seemed like the thing to do with the avatar design system, picking out some hairstyles and lip color on a cartoonish avatar and just randomly clicked on a button that said random. This changed my cartoonish avatar into a beautiful photo-realistic brunette in a nice office style outfit. I decided that an excellent place to stop with avatar designing.
You can add a voice to your avatar in several ways, one of which is text to voice. The text to voice system is really excellent. I wish I could get it to read stuff to me, like for instance an entire book.
The avatar doesn't walk around in the 3D space; it's a head in a window next to the 3D scene.
You can add the application to networking sites like facebook or myspace. I've got one on my facebook page.
I suspect there is a potential market for 3D build it yourself systems like this. Manufacturers and retailers can pay to produce the 3D shapes, you put them in your space as decorations, when people visit your space they serve both as decorations and ads.
Add in some "real" avatars, text chat, voice chat, music sharing, something like this might be a hit.
Note to those that try it: the "Save Scene" button is on the 3D View tab.