I dusted off the G1 phone from the drawer and decided to give it a go again because of the recent news on Google Latitude, an update to GMAP 3.0+. Basically, it gives away your position via GPS or GSM network and allows you and your friends to see each other (kinda like Loopt on the iPhone,... actually just found out Loopt is available on Android Marketplace as well, pretty cool actually).
I haven't played with this a heck of a whole lot, but in short this is what I know and seen:
1). To install it, wait for your G1 to signal you for an update. As for me, it was a 2-part update. The update process was poorly organized. It can't be manually triggered in settings for system update. You just have to play with your phone until suddenly you are prompted with said update. After part 1 has been completed, my phone didn't automatically start part two. Again, after playing with it for a bit, it prompted me for part 2 of update. (Note: I have a developer Android firmware so my experience may be different than T-Mobile G1 customers).
2). Latitude resides within GMAPs on G1. You'll see a new icon in the middle of the menu bar with GMAP. Clicking on it allows you to invite friends and see friends who are already in your list. Those with a Google account will be tied seemlessly (you can IM and see their status, etc...).
3). Those with G1, BlackBerry and WinMo should be able to get on Google Latitude. iPhone guys may have to wait a while until this gets pushed out in a new firmware release. If you have non of te above, you can still use your PC and hookup via iGoogle gadget. I'll continue to play with this for a few days and report back.
If you'd like more info, visit:
http://www.google.com/latitude/intro.html or point your mobile browser to: google.com/latitude