Point Safari at m.google.com/latitude, let Google use your location, and Bob's your uncle. Your location shows up on a Google map within the browser, with Latitude appearing as a tab next to Gmail and GCal. Add friends by choosing from your Gmail contacts or typing in their email address and they'll receive a link to the mobile site, where they can sign up themselves and view your location.
You can switch between map and satellite view and get directions. There's an option to view traffic, but this wasn't working when we tested it.
Clicking a contact's icon presents the option to send an email, get directions to the contact's location, and change the precision of location information you'd like to share with the person. The options are 'best available location', 'only city-level location', and 'hide from this friend'. Because it's an opt-in service and you have to invite or approve anyone before they can see your location, we don't see any privacy issues. You can also turn your location off at any time.
We went out
for a bacon sandwich to test Latitude and the service worked well, although it does rely on the accuracy of your GPS. Google gets around Apple's inability to run apps -- even browser-based -- in the background by updating location when you launch the app, while it runs in the foreground.
We love Latitude. It would be perfect for keeping track of your mates at big events such as festivals -- like Latitude, boom boom! -- if the mobile signal and GPS were up to it.