Geolocation in Austin

In Austin, Texas, things are happening at the SXSWi (South by Southwest interactive Festival), as they have in the past (this is where twitter made its first big splash).  Geolocation is one of the hottest topics--how do you "check-in" with your friends virtually at different spots and announce your own location?  Two key players in this area are Foursquare and Gowalla.  For more info, see http://news.cnet.com/8301-13577_3-10466901-36.html?tag=mncol;txt