GPSWeb, a Firebird extension that adds a User-Location header to every HTTP request, allows you to automatically send your location (as GPS coordinates) when requesting a web page, rather than relying on site-specific cookies. The comments suggest that future versions of the browser/extension could handle lists of 'trusted sites' to which the location information should be provided.
If the browser can handle this kind of personal information, and only send it to trusted sites, it should be easy to extend this to FOAF data, personal preference profiles and other semi-public information.