Twitter rolls out geolocation, and Facebook location sharing is coming
We already knew that Twitter's move was coming, because Twitter's location services have been part of the API and available in third-party apps for some time now. TechCrunch is reporting that geolocation was only on for Twitter.com temporarily, but that it should come back within the week, in time for SXSW. They've also got screenshots, in case you're a "believe-it-when-I-see-it" type.
All of this points to the idea that location-centric apps like Google Buzz and Foursquare aren't just a passing phase. Get used to location in social networks, because it looks like it's about to arrive in a big way.