Good move for Loopt, but as I understand it it's a closed system for their users. The better approach is from Localmind, which just won the startup competition at Where2.0 yesterday, and can use checkins from not just Loopt but Foursquare, Gowalla, Facebook Places, and others to be created to do the same job. See Scoble's video reviews from SXSW, or just download the app. This is the first iteration of Location which gets me juiced.