[jffry]

Would this be something like Google Latitude, where I share my present location (privately, limited to you, a select group of friends, Google, and the NSA; or openly, à la Foursquare or Twitter)?

Or are you envisioning a phone-book-like service where I post a more general "I live here" sort of thing?

I would not participate in such a service. It's arguably much more invasive than a phone book - for one, phone books are usually only available in that geographic vicinity, and are not readily searchable like an online service would be.

[slice-of-tree]

It would be something more open, like Twitter.

And, FYI, most phone books actually are available to search on the internet. E.g., for the UK: http://www.thephonebook.bt.com/publisha.content/en/search/re...