>Or heck even for that matter, any idea how to make a small
>robot follow/chase a person ?

TPA81 octal passive IR detector. Based on different principle then 
pyroelectric sensors, but sensitive at the right wavelength:

http://www.robot-electronics.co.uk/shop/Thermal_Array_Sensors2086.htm
Also supplied by:
http://www.snailinstruments.com/eng/robotics/

Perhaps combined with IR or ultrasonic ranger to keep the robot at 
the propper distance required by etiquette :-)

Josef

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