This weekend The Register published an article named Google developing eavesdropping software. The article describes how Google uses existing PC microphones fingerprinting technology to show relevant ads that appeal more to you. The article goes on to explain how the sound fingerprinting works; it "breaks sound into a five-second snippets to pick out audio from a TV, reducing the snippet to a digital "fingerprint", which it matches on an internet server." Privacy folks are worried about the repercussions of such software.
Postscript Barry: I should link to Google Paper Explains Listening To Your TV Can Help It Put Ads & Info On Your Computer we covered back in Jun. 9, 2006.