Geocaching, the game of finding objects hidden around the world using a GPS device, is believed to have 5 million participants worldwide, according to leading commercial portal Geocaching.com. That company released a new geocaching app for Android this morning, with a price tag of $9.99.

With more than 5 million participants, Geocaching.com calls the practice "the most popular location-based game on Earth." That's a number not for one particular company, but an estimate of all the geocaching participants across different platforms. Still, the game is typically thought of as a pretty nerdy pass-time, but it remains twice as big as the much hyped location startup Foursquare. Are we Foursquare fans missing out on something?

While Foursquare in particular has garnered a huge amount of media attention, it is just one of many different types of location-based services. As a service based on social sharing of your location, it may be less appealing to many people than are other service that leverage, but don't share, where you are. Location based social networks may be more difficult for people to understand, as well.

Foursquare relaunched yesterday with a new emphasis on features that could be described as geofencing: an option to receive push notifications from trusted sources or to-do items when you check-in within a certain proximity of associated locations. That's an important differentiator between the startup and the new Facebook Places. Might Foursquare implement a geocaching-type feature as well?

One thing's for certain, these new location-based social games are more interesting, more innovative and more compelling for technology-focused press to talk about than old fashioned (10 year old) geocaching. More people appear interested in playing geocaching so far, though.