Why Facebook Should Acquire Foursquare - Caleb Elston
calebelston.com
calebelston.com
I think the best positioned player in the mobile location based service space is Apple. They are well positioned to get paid well, no matter what service ends up winning over the most users.
I agree with you about critical mass.
It looks like more of a Facebook application than an integral part of Facebook.
I think he might think twice before selling to anyone based on that experience.