Google Latitude knows where you are…and no it doesn't use GPS or Cell tower triangulation

Perhaps some of you have heard of a Google program called Latitude.  It is an application you can install on your Blackberry, Windows mobile phone, or laptop.  This tool is simply amazing at locating you.  It uses GPS(obviously), cell towers through triangulation, and Wifi through triangulation.  The one I really want to discuss is the Wifi locator.  
The other week I brought my laptop to a client site in Phoenix.  I fired it up and was amazed to see that it actually knew where I was located.  Now I don’t have GPS in my laptop and I had not used my At&t connect card.  I was amazed!  How did this thing know where I was?!  Amazed by this I immediately Googled how Latitude finds you.  Now Google doesn’t have an official announcement on their secret sauce and how it works.  But I can only assume that when they were driving around creating their street view application(another amazing app by the way).  That they also created a huge database of wifi access points and their signal strengths.  This way they can analyze the wifi signal strength of your PC and query it to their database.   This way they could triangulate your position.  Now I’m assuming they use other variables as well like what your public IP address is to first determine what area you in.  Either way this technology is very innovative whether you agree or disagree with this from a privacy perspective you have to admit this is a thumbs up for Google’s intelligence.