A couple of months ago I started noticing a couple of Facebook friends enthusiastically posting their latest accomplishments on Foursquare. I paid no attention. But they stayed enthusiastic and kept updating. I noticed that.

Then I started noticing Foursquare’s name showing up in the early and not-so-early adopter press. Hmmm.

So, yesterday I downloaded the iPhone app (about 12 seconds, amazing interface) and the Blackberry app (beta, go to the website, copy the link, blah, blah, blah, not 12 seconds – come on BB, apps are killing you but I digress).

Foursquare is game/twitter/crowdsourcing/yelp/tripadvisor all rolled into one. You visit places. Check in on your smartphone to let your friends know where you are. See who’s nearby. Write a review. Collect points. Get famous. Move on.

If necessary, in the morning, you can even figure out where you’ve been.

From a business perspective Foursquare’s got some pretty mighty business implications. Slow night? $2 off promotion for Foursquare users. Just show them your iPhone. Get listed in the what’s hot. Get dissed in the reviews.

It’s early days but Foursquare clearly foreshadows more of what’s coming as mobile and other social technologies keep moving forward. Together. Fast.

The founders of Foursquare are moving forward too. It’s clear that content, advertising and (from a business perspective this is big) analytics are going to be key new elements of the Foursquare platform.

Check out this Slide presentation if you want a better feel for Foursquare