I would think that facebook (and their mobile apps) are a bigger threat than google. They could add a 'share my location with friends' feature that would be competitive.
Soon we'll see posts about sama eating breakfast (<a href="http://paulgrahamatebreakfast.infogami.com/" rel="nofollow">http://paulgrahamatebreakfast.infogami.com/</a> )<p>In all seriousness though, glad to see Loopt is doing so well.