A french lab, who published a paper at Siggraph 2007, is working on a impressive markerless tracking/modeling system, the GrImage Platform:

This architecture is designed for mixed reality applications requiring such dynamic models, tele-immersion for instance. (…)

The acquisition [is] based on standard firewire cameras; the computation, based on a distribution scheme over a cluster of PC and using a recent shape-from-silhouette algorithm which leads to optimally precise 3D models.

[youtube]http://youtube.com/watch?v=ZG53YDVW1Ik[/youtube]