Three years before Facebook bought Instagram for $1 billion this week – one and a half years before Instagram was even created – there was Foursquare, launched in Spring 2009.

Then as now, Foursquare was an app for people that wanted to "check-in" to locations and tell their friends where they were at the moment.

It was, back in 2009, the most exciting new social network since Facebook, and one of the first devoted entirely to the mobile platform.

At SXSW, the conference where Twitter famously gained the moment that ultimately propelled it into a $10 billion company, Foursquare dominated the conversation in both 2009 and 2010.

In the months and years that followed, CEO Dennis Crowley fielded a small acquisition offer from Facebook and a much bigger, two-hundred million dollar offer from Yahoo, both of which he rejected. In that time he accepted two rounds of funding from pristine venture capital firms USV and Andreessen Horowitz. Foursquare's last round, a $50 million raise in June 2011, valued the company at $600 million.

It's starting to look like all that hype was unwarranted.

Foursquare is no longer the only social network built for the mobile Internet user – now there is Instagram and Path and a few others – and it is definitely not the most exciting new social network since Facebook; that's Pinterest.

The biggest problem for Foursquare is that, compared with other mobile social networking products, not that many people seem to use it.

On its about page, Foursquare says it has 15 million registered users. By comparison, Instagram has 35 million users.

According to AppData, 570,000 people share Foursquare data into Facebook every day, 3 million every month. Pinterest, which only launched in 2010 has 1 million users sharing data with Facebook every day, and 10 million sharing every month. For Instagram, the numbers are 2 million and 11.5 million.

Apple's iTunes store doesn't expose how many times an app has been downloaded, but one rough measurement of an app's downloads and user engagement are the number of reviews users have written.

Here's a comparison of social apps using this metric:

Here's the same chart with scale-breaker Facebook removed. Foursquare still comes in behind younger apps Pinterest and Instagram, as well as Yelp, a Web-first rival. (Path seems to be another very over-hyped startup):

Simply put: not that many people are using Foursquare, certainly not compared to the amount of people using Instagram, Pinterest, or even Yelp.

The good news for Foursquare is that CEO Dennis Crowley wisely capitalized on the app's early hype to raise a boatload of cash last summer (with minor dilution). Foursquare only has about 100 employees right now, and with $50 million in the bank, it can probably afford to keep them employed for another three or four years.

The even better news for Foursquare is that investors and executives know the company needs to pivot in some way, and they are trying to figure out how.

One idea we've heard is being floated around is to turn Foursquare into more of a Web company and less of a mobile-only platform. It could be something like Yelp or MenuPages.com – with a search engine-friendly Web page full of user-reviews and tips for every restaurant on the planet. That's a good idea, especially since Foursquare tips are very useful.

That kind of pivot would also make Foursquare a more useful product to the majority of users out there who just want to consume data, not create it through a gimmick like "checking-in." (Likewise, most YouTube users don't upload videos; they just view them.)

The only downside is that Foursquare investors probably were hoping the company would turn into more than another Yelp. Yelp, now a publicly traded company, has a $1.5 billion market cap. Venture investors expect more than a 3X return. But then again, there are worse fates for startups with lots of early hype and little user-adoption three years in.

Related: How Dennis Crowley created Foursquare >>