I mean, don't get me wrong - I love pwning chumps with my Vampire and sharing my music taste via iLike, but I don't want to join your causes, compare movie tastes or join your Entourage. I'm not saying opening up the platform to developers was wrong... In fact, it's the evolution of the internet, so I haven't stopped chanting "power to the people".
But I can say that filling the center of my page with garbage, err, "targeted ads", is not what I'm used to. And when you start messing with the formula that made you successful you'd better have some really strong content to keep me coming back, not just silly, useless third party apps. I'll also add that most of the ads I see are completely irrelevant to my interests. Ouch, that hurts.
"There has to be another explanation", you say? Sure. How about this: Follow the kids. While the recent data shows "old married guys" are joining Facebook by the thousands, which very well may be a legitimate reason for not wanting to hang out with Dad, think about this common sense fact -- the college and high school kids on the site don't have as much time to spend on the site because they're back in class.
Here's a simple formula on how to lose visitors for future social networking sites targeted at 18-24:
Lack of relevancy + creepy old men + school starting = Less time online
Update: via Valleywag is this priceless quote from Jason Calacanis. Sure, he owns Mahalo, so there is a minor conflict there, but it's dead on:
"Social networking is second only to chat rooms as the worst place to advertise. The content there from your friends and your family is more compelling than any advertisement. Google has the greatest advertising in media history -- search advertising. When you type a word into the box, we know what you're looking for. When you're on Facebook, we know you're looking to meet a girl or talk to your friends. It's a terrible platform for advertising. The holy grail of e-commerce forever has been that people are going to buy something online because their friends did, or that everybody here is into skiing so we're going to sell a bunch of skiing stuff. It hasn't happened. Plus, e-commerce is a low-margin business. It's nowhere near search inventory."