A button just above the message area lists all the businesses nearby, also listed by proximity. You can choose the restaurant or store you're at, or choose the "best available location" option. That's powerful, because GPS is only approximate.

You can choose or you can reveal your general location or specify exactly which building you're in, all with a click or two. To the best of my knowledge, it's not possible to exactly specify nonbusiness locations, such as your home. That's probably a good thing.

All that sounds vaguely similar to location features on Twitter, or location apps in Facebook. But those implementations are vastly inferior, and far less immediately usable.

More important, I believe Google Buzz will trigger a culture-changing "network effect." That's where a snowballing of usage occurs: The more people use a network, the more valuable it becomes; the more valuable it becomes, the more people use it -- just like, say, the Web, e-mail or cell phones.

Google Buzz on a PC is a closed experience in two ways: First, you need Gmail to fully experience it. Second, you get messages only from people you're following. With Google Buzz on a PC, you're blind to non-Gmail users, and also to everybody you're not following.