I worked in computer vision for my MSc three years ago, and based on the state-of-the-art at that time I would be surprised if Natal going to be as robust as the mass market expects. This kind of thing is notoriously hard and error-prone. The information coming in from cameras is often so noisy and incomplete it is very difficult to tell what you are seeing.
Also the rumour that they have chopped Natal's onboard CPU and moved most of the processing to the Xbox 360 CPU does not fill me with optimism... Prove me wrong, Microsoft, prove me wrong!
When Natal was unveiled at E3, it was having exactly the kind of issues I expected: http://www.youtube.com/watch?v=NKtpJW9pg84
Also the rumour that they have chopped Natal's onboard CPU and moved most of the processing to the Xbox 360 CPU does not fill me with optimism... Prove me wrong, Microsoft, prove me wrong!