Not much to say other than this is a new mobile maps application. Have a look at the introductory video below.
For a list of supported phones, check here. The iPhone and iPod Touch are in the “coming soon” category, which is a suprise and a short term negative. You can visit google.com/latitude on your desktop and install the Latitude iGoogle gadget, which lets you share your location from your desktop computer.
As far as supported countries go, currently there are 27 of them.