It's coming "holiday season" this year which is no surprise. Meanwhile Andrew Fitzgibbon confirms Natal captures stuff "30 times a second."
"Scheduled to be available in holiday season 2010, ‘Project Natal’ is only the most recent example of Microsoft’s work creating natural user interfaces,” read a Microsoft press release, reports . This comes from the Consumer Electronics Show 2009.
Andrew Fitzgibbon is Principal Researcher of Microsoft Research, and he spilled during CES 09 that what Natal does, "is it evaluates effectively trillions of body configurations every frame. We’ve made it do that 30 times a second.”
Hardware and software capture the body. Whether it could actually support games that run at 30 frames a second remains to be seen given the latency of motion translation. We'll just embrace ignorance for now and go with 'sure, why not?' for 30fps.