MySpace is so 2005. And Friendster? Does anyone even remember when that was cool?

Ah, yes, social networking sites. How quickly they catch on, and how equally quickly they fade away. Inherent to them is what I think of as the Pokemon Problem: at first, people set out to ‘collect’ all of their friends. They use the site frequently, connect and counter-connect. And then, after a little while, the ‘collecting’ slows down. They’re connected to all of their real-world friends, and probably to a slew of random people they could care less about as well. At which point, they have far less reason to come to the site. Sure, they could message friends through it; but they already have their real friends’ email addresses, so why bother? And photo sharing? Doesn’t Flickr already do that far, far better?

So the site begins to atrophy. User pages become unchecked hulls, perhaps logged into every few weeks just to see if anything interesting has happened. Ad revenue falls, user sign-ups dry out, and visions of billion dollar acquisitions no longer dance like sugar plums in the founders’ heads.

But, of course, there’s a point at the peak where a savvy exec team could handily cash out of such a site. For which reason, new social networking sites still pop up all the time.

At the moment, the gorilla ‘new kid’ is Facebook, already hugely popular with the college crowd. But, like any of its forebears, once chasing a market that doesn’t have time to log in eight or nine times a day just to profile-stalk the hot girl in chem class – and Facebook, indeed, is now trying hard to expand to the ‘grown up’ world – the site will run into the same problems of short shelf life.

Even in the case of Facebook, their best efforts of pushing into that ‘grown up’ market will likely be feeble indeed. Sure, my peers and I will perhaps join up. But my parents? My grandmother? The vast majority of the online market? Not a chance.

So, if the model of a social networking site is to grow fast and sell at the peak, and if the market of young whipper-snappers is already tapped, couldn’t a site make a huge amount of money by being the first to successfully target the 34-65+ demographic? I suspect one could. The question, then, is what kind of social networking site my mother and my grandmother might join.

Behold: Geni.com, a social networking site disguised as a snappy, AJAXy, web-based family tree application. You can start filling out what you know about your relatives yourself, then (and here comes the clever viral part!) enter the email addresses for any of those family members to invite them to help continue fleshing out the tree.

As the success of the Mormon Church’s Family History Centers as proselytizing tool suggests, people of all ages are fascinated by their past, and eager to map out their biological place in the world. Plus, Geni’s investors and exec team are extremely seasoned, savvy, and press connected, so a slew of coverage – the first step in getting this otherwise virally self-spreading effort rolling – is likely just around the corner.

Get on and sign up fast. You don’t want to be the slow cousin at this upcoming digital family reunion.