When reading the post related to Google's ad targeting policy
http://blogoscoped.com/archive/2007-08-01-n50.html

it appears that Microsoft _really_ has different plans when targeting advertisements.

Microsoft is planning to use "cameras, remote controls and biometric sensors to detect the identity of the person viewing a TV, cellphone, or computer monitor display. "

Link to the patent application:
http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.html&r=1&f=G&l=50&s1=%2220070174117%22.PGNR.&OS=DN/20070174117&RS=DN/20070174117

Source:
http://www.techdirt.com/articles/20070730/162255.shtml