With an admitted android bias, I'm having a hard time seeing why someone would pay $5-10/mo for this, working only on IOS4, instead of using Google Latitude for free, on any number of supported devices.

Latitude doesn't support the manual geofence alerts, but it does have its own automated alerts, the pros and cons of which are up for debate. For many people, though, not having to set up and curate alert settings may actually be a welcome convenience.