Introduction to Google Latitude (1’25’’) + Privacy Settings (2’15’’)

Not available on the Iphone yet though. More here.

Update: given the sensitivity of location info, Google made sure to add a privacy video as well:

I guess the main problem will not be that users do not have control over what they share or not… just like in Social networking sites, it might become socially awkward not to share back when someone requests access to your info. So you ‘ll end up sharing location info to a much larger audience than you initially had in mind…