It's not clear why Yu is leaving now. He raised nearly $500 million for the company, and was looking for more. But a few things are known: Zuckerberg has repeatedly said that the company's focus is on growth rather than making money. He has made a habit of quickly cycling through executives. Former Facebook COO Owen Van Natta, who left after an apparent demotion, is a notable example.

The question is who's next? Jonathan Heiliger, a dotcom-era Internet wunderkind now in charge of Facebook's vast technical infrastructure, has long been said to be restive. COO Sheryl Sandberg, the Google veteran splashily hired last year, might be called to account if Facebook's sales don't catch up with its user growth. As the door to Facebook's executive suite keeps swinging, it seems like only a matter of time before people start asking questions about the prickly, isolated 24-year-old at the top.

That's why, for days before it was announced, top executives at Facebook desperately hid technical lead Dustin Moskovitz's plans to leave. They dithered as Mark Zuckerberg tried to persuade his cofounder and college roommate to stay, and others, led by COO Sheryl Sandberg, concocted a plan to spin his departure. That spin has now been dutifully printed in the pages of the Wall Street Journal: Facebook's changes are the "type of evolution you see among young growing companies and specifically young growing companies in Silicon Valley," company flack Larry Yu told the paper.

Sandberg, who closely directs the company's PR, would have us think that the uproar that has taken place at the social network since her arrival is a healthy evolution. It is not. The internal politicking she has introduced to the company is destructive, and has sent many of the company's best and brightest fleeing. The list of the departed includes data guru Jeff Hammerbacher, product VP Matt Cohler, platform director Ben Ling, and most recently, Justin Rosenstein, a top engineer who's leaving with Moskovitz. Operations VP Jonathan Heiliger may be next. The defections all hurt. But most of the blame lies with Zuckerberg himself.

Zuckerberg has always styled himself as the company's "founder," relegating the likes of Moskovitz and Chris Hughes, now Barack Obama's Web campaign director, to "cofounder" status. Never mind that this distinction doesn't exist in English; those who start a company are all equally founders.

Zuckerberg clearly considers himself first among equals; he once referred to Moskovitz as "disposable" and a "soldier." The former Harvard roommates patched over those insults, and Zuckerberg said he will rely on Moskovitz's counsel even after his departure.

If Moskovitz really thought he could guide Facebook's evolution, he would have stayed at the company, right? Zuckerberg has a history of churning through confidants. Napster cofounder Sean Parker helped establish Facebook in Silicon Valley as its president, only to be disappeared from the company. Former COO Owen Van Natta was in favor, then out. Sandberg had his ear for a while, but may be losing it. Lately, I hear he favors Christopher Cox, the twentysomething recent Stanford grad he recently tapped as the company's director of product. We'll see how long he stays by Zuckerberg's side.

This fickleness may be predictable from a 24-year-old. But it's fundamentally bad for the company. Yahoo thrived, in its early days, on the partnership between CEO Tim Koogle and founders Jerry Yang and Dave Filo. Google's triumvirate of its cofounders and CEO Eric Schmidt improved on that management form; the troika lends the company some stability by making sure decisions at the top are never unilateral.

Zuckerberg's insistence on the "founder" title suggests that he always planned to rule the company alone. It's a bad plan. His instincts on what kind of website will attract a 100 million users have been spot-on. But he has no business sense. At one point during the Facebook redesign process, he suggested getting rid of advertising altogether, having grown disillusioned with both old-style banner ads and the company's experiments with targeting ads to users' behavior.

Will Zuck ever find an equal partner, a sounding board who can help him turn Facebook into the large, ongoing concern he envisions? Dustin Moskovitz may not have been the right person. Nor, it seems, is Sheryl Sandberg.

Yet to staunch the bleeding of Facebook's technical talent, Zuckerberg will have to find someone to ground him — someone for whom he has enduring respect, who can moderate his worst impulses. Without it, there will be one word describing what's going to happen to Facebook: "founder."

Heiliger previously worked for Andreessen at Opsware. One would think the chrome-domed entrepreneur, now chairman of Ning, would prove a powerful ally in the fierce political battles that have roiled Facebook since the appointment of Sheryl Sandberg, a Beltway insider turned Internet executive, as COO. Nothing's certain, and Heiliger may well stay. But for him to be so unhappy as to openly entertain job offers? The social network's executive suite seems to be coming unplugged.

Valleywag's coverage last week of Sandberg's spinning in response to the departure of a key employee was deemed, in some quarters, a "character attack." Yet Sandberg's character is the very issue here. Her response is very telling: First, she wrangled a long followup story from her frequent dinner guest Kara Swisher that called our story sexist, over-the-top — and factually correct.

Swisher's report is damning for Sandberg. It acknowledges that Facebook executive Matt Cohler, who left to join Benchmark Capital, was unhappy with Sandberg's leadership. It reports that Jonathan Heiliger, the company's infrastructure chief, has also been unhappy with Sandberg — Swisher errs only in saying that the two have patched things up. Swisher's new report also means that the version of Ben Ling's departure fed to her by the company last week was false.

Facebook executives have acknowledged all these facts. But characteristically, Sandberg has steered the discussion away from the real problem — the bad decisions she's made, the poor judgment she's demonstrated — and toward massaging reality. She is, even now, planning a new PR campaign to buff her image.

Did it ever occur to Sandberg to figure out why she rubs so many of Facebook's technical leaders the wrong way? Could it have anything to do with her meddling in matters that CEO Mark Zuckerberg has said aren't her job? Facebook has real problems in Sandberg's area of responsibility. Billing, customer service, and other mundane-but-critical aspects of the social network's advertising operations are chaotic, and require fixing. Sandberg's moves to shore up her image suggest the real reason for her unpopularity within Facebook: Her overwhelming concern for style over substance. How ironic that that pointing that out has sent Sandberg spinning.

Our site is similar to a typical Web three tier architecture. We run a collapsed Web and app tier on the top, which is Apache and PHP, both tremendous open source projects. The mid-tier is memcached, which is an open source in memory, distributed cache. And then the data is persisted and stored in MySQL databases — again, open source technology. Around that we have a number of other applications that we've developed in-house.

We're sure, however, that many of our fine readers will understand all this and might even find it interesting. If so, view the clip below. Then please, when commenting, do that thing where you write in code. It's neat!

Data Center Knowledge has already identified some of Heiliger's investments: new multimillion-dollar datacenters are going up in Ashburn, Va. and Santa Clara, and Rackable, a maker of servers, is receiving a large chunk of Facebook's hardware budget.

But I'm more amused by the money Heiliger didn't spend. On his honeymoon, that is. In 2004, he and his fiancée Germaine Yokoyama hit up wedding guests to pay for a trip to Venice.

(Photo by Jonathan Heiliger)