Is my Mac spying on me?
If you've ever used Photo Booth, or any other app using your built-in camera as a source, you may know that there's no way anything less than 1 second is fast enough. There is a very obvious warm-up time in order for the camera to actually warm up and provide an image. Although the problem with timing Photo Booth is that it has to open the app, draw the window, then fire up the camera somewhere in there.

As a matter of testing, I opened up Quicktime Player (Quicktime X) and let it settle down, then I hit File -> New Movie Recording. Luckily for me, the image didn't fire up right away because the built-in camera for my laptop was chosen, but I have the lid closed using an external screen also with a built-in camera.

So I changed the input source to the external camera, and pressed start on my stopwatch as soon as the green LED lit up (which was pretty much immediately). The video started displaying at about 1.5 seconds in. That's still certainly within "blink-and-you'll-miss-it" territory, but only barely.

My answer is that I'm suggesting stray light may be reflecting off of area the LED resides in, invoking an "illuminated" feeling, but that nothing may be happening in reality.

However, I don't suggest that you do nothing. Commercial vendors such as Sophos offer Antivirus products of OS X, Lion-compatible and free too in Sophos' case, and I've also used ClamXAV as a one-off scan-on-demand utility when I've had similar feelings (or when I've wanted to check a file for a windows-using friend, etc.).

Note also that OS X does have built-in spyware protection named, "XProtect", that was born out of the "MacDefender" trojan scare. TUAW has many great articles on the subject under the security tag.