The founder and CEO of Plancast Mark Hendrickson decided to stop working on the effort full time and wrote a detailed post mortem in January. The service was about sharing your plans with others. Here's what he said about how geography mattered. This reads like the post mortem of many other social network startups that didn't make it.
Geographic specificity is another inherent limitation to a plan’s value. Unlike virtually all other content types (with the exception of check-ins), plans provide most of their value to others when those users live or can travel near enough to join.
I may share plans for a ton of great events in San Francisco, but few to none of my friends who live outside of the Bay Area are going to care. In fact, they’ll find it annoying to witness something they’ll miss out on. Sure, they might appreciate simply knowing what I’m up to, but the value to that kind of surveillance is rather modest all by itself.
This is especially problematic when trying to expand the service into new locations. New users will have a hard time finding enough local friends who are either on the service and sharing their plans already, or those who are willing to join them on a new service upon invitation. People who encounter the service from non-urban locations have the hardest time, since there aren’t many events going on in their area in general, let alone posted to Plancast. Trying to view all events simply listed within their location or categories of interest yields little for them to enjoy.