This has been going on for years. See wardriving: http://en.wikipedia.org/wiki/Wardriving and Wigle: http://wigle.net/
Or is it only a problem when Google does it?
Honestly, it doesn't concern me that much, but I'm trying to figure out what has other people worried.
"People have been spilling oil and gasoline in their driveways, where it gets washed away and makes it way into the oceans, for years. Or is it only a problem when Exxon does it?"
Badness is not all or nothing. It can depend on how widespread something is. Google operates at such a large scale that many things they do can be bad, even if they are not bad when done by individuals.
My point is that if you're concerned about the privacy implications of an access point database, you should be concerned no matter who's putting it together.
Not necessarily. But it is MORE of a problem. Google like to scale. They also scale problems. Globally.