One of the relatively unsung features of the upcoming iPhone 3.0 firmware is that the new version of Safari for iPhone will use geolocation. This means that the browser can request location information from the iPhone's GPS receiver, and can also provide that location information to websites that you're visiting.
ComputerWorld's Seth Weintraub reports that the beta versions of the firmware are working well with sample web-aware websites. This capability is not only planned for the iPhone's implementation of Safari, but many upcoming browsers for Mac as well.
Geolocation capabilities make it simple for developers to create web apps that no longer need to ask you for an address or zip code. Google, for instance, is planning on making their Latitude application a 3.0-only web app rather than a standalone application on the iPhone. Latitude will leverage the geolocation features of Safari by knowing exactly where you are at a particular point in time and sending that info to the Latitude servers, then returning the whereabouts of your friends while informing them where you are.
For those of you who don't want your 3.0-enabled iPhone to let the world know exactly where you are, remember that you can always turn off Location Services in the General Settings or just answer "Don't Allow" when asked if Safari or a particular website would like to use your current location.