“You hit this limit, and you have to commit Facebook murder, or perhaps ‘culling’ would be a better word,” said Sreenath Sreenivasan (5,000), dean of student affairs at the Columbia University Graduate School of Journalism. His page bears the admonishment, “FB will not let me add any more friends,” and he periodically posts a message asking some on his list to “unfriend” him.

What may seem surprising is that the subset of people with sizable lists is not limited to unemployed 20-somethings, commandeering tables at Starbucks and deluding themselves that they’re “networking,” social or otherwise. The high-users include plenty of grown-ups with real jobs and, seemingly, better things to do with their time than updating their “status” for strangers, former colleagues and camp buddies from 300 years ago.

“At one point, I arbitrarily decided that for every new friend I confirmed, I had to delete one, like people with small closets do with their clothes,” said Kurt Andersen (3,072), the host of “Studio 360” on public radio. “I devoted an entire weekend to going through them. But it made me feel like a 14-year-old girl: ‘I’ll be friends with you but not with you.’ ”

Facebook friends grow like kudzu for a variety of reasons, often personal or professional marketing  a proxy for the exchange of business cards (so old school). As in life, social networking lends itself to expanding social circles with like-minded people, so there are autologous Facebook cabals for foodies, literati, political junkies, perhaps gardeners, probably plumbers, definitely Civil War re-enactors (whose membership seems to be self-selected from former high-school audiovisual clubs).

Jeffrey Toobin, a CNN legal analyst, credits (or blames) the election of 2008 for his Brobdingnagian list. “During one of the many primary nights, there was a shot of me from behind in the studio,” said Mr. Toobin (5,000). “Some intrepid viewer did a freeze frame showing that I was on Facebook at the time, and put it on the Web to make fun of it. Fair enough, but that mockery went viral. I now have 1,500 people pending, and I feel like I’ve declared Facebook bankruptcy. It’s the 21st-century equivalent of ‘12:00’ flashing on my VCR.”