From the Web 2.0 Conference:
3B already makes a system that lets you browse collections of Web pages in 3D. The original product was designed for commerce sites to mimic the experience of shopping in a mall. In other words, Doom meets American Express. New for 3B at the Web 2.0 conference is the ability for users to create their own 3D spaces into which they can insert personal photo-archive pages, pages from social sites like MySpace, or pages from any site whatsoever. Now, it's Doom meets Del.icio.us. Users will also be able to create avatars and hang out in their space with other users and their avatars.
3B is clearly taking on Second Life, by focusing on making it easy for users to create their own little virtual worlds--little virtual asteroids, really--instead of staking out real estate on a pre-existing, virtual planet.
3B isn't nearly as flexible as Second Life. Your individual "world" is only a bunch of Web pages projected onto the corridor walls in a pre-laid-out virtual building. And while it's much easier to learn how to navigate 3B than Second Life (a plus), viewing a 3B site does require that you download and install the 3B software (which may keep users away).
I get queasy when I use 3D Web interfaces, but the next generation of humans may adapt to this navigational system better than I have, and find this physical metaphor for Web navigation actually useful and interesting.