Lesson: Always read the fine print
Foursquare is "a location-based mobile platform that makes cities easier to use and more interesting to explore. By “checking in” via a smartphone app or SMS, users share their location with friends while collecting points and virtual badges."
I don't have a smartphone so I'm SOL... nice. While I understand the concept, knowing this I find it even harder to believe it's going to be a measure of Social Media. According to TechZone360 about 1/4 of a million people use smartphones, primarily for the internet. Considering there are 310 million people according the US Census 2010, that means .16% of the country is even eligible to be social media savvy. According to Internet World Stats over 77% (240m) of the US population are connected to the internet now. Facebook has more than 750m users (over twice the US population); Twitter passed the 300m mark recently. In comparison it seems Foursquare is barely a drop in the bucket --hardly worth market research just yet.
Will I keep my account? Of course, sitting idle does nothing. Looking at the various options, a lot of other users, channels and add on's have been idle for a while too.
Recommendation, unless you have a smartphone, don't bother. If you do, still not sure it's worth your while. Wait for version 2 to come out. Maybe Google+ will add something to it's circles to do the same thing.