To elaborate a bit, I did look into SimpleGeo for http://mopho.to but one of our biggest needs getting started was access to existing place data which GeoAPI has available right now. I've been keeping an eye on SimpleGeo for news about their upcoming market place where you can purchase data sets, but it's been a few months and it's still unclear when it will be available. I haven't done any comparative benchmarking yet since GeoAPI met our needs and SimpleGeo wasn't ready yet.