Media Machines makes a 3d plugin specifically designed to be embedded in webpages and allow you to share 3d environments with others. One of the key movers behind it is Tony Parisi, who has a long history with VRML technology. Among other things, you can import SketchUp models into their 3d scenes.
They just landed $9.4m in funding, and their website says they’re hiring “virtual world system” folks.
The interesting thing about this, of course, is that here’s something that could be a “universal client” for web-based 3d worlds. Media Machines doesn’t seem to have a horse in the server race. Yet, anyway.