Geolocation API Research

I’m starting to do some research into geolocation APIs. Right now, I’m planning on checking out the Google Gears and Google Chrome APIs, the new Firefox 3.1 APIs, Skyhook’s technology, and IP geolocation technology like that used by ip2location. Anything else you think I should be looking into? How valuable do you think geolocation APIs on the desktop are? Will all computers (or at least all laptops which are gradually becoming all computers) have GPS chips soon? Other than GPS, IP addresses, Wi-Fi access points, and cell tower triangulation, how else can people be located?

Any and all feedback is greatly appreciated.