As Facebook introduces "frictionless" media sharing, epic Timelines for every user and continuing "engagement" land-grabs beyond, Mark Zuckerberg's dorm-room project is becoming, quite simply, the media world's black hole, and effectively devaluing the rest of the non-Facebook web in the process.

To grasp exactly what Facebook is doing to the web ecosystem, it helps if you picture it as a real place. Imagine you're at a bar where all your friends hang out -- where everyone knows your name. For the sake of argument (and visualization), let's say it's the bar from "Cheers." Or maybe it's Paddy's Pub from "It's Always Sunny in Philadelphia." (Whichever one Facebook tells you your friends are watching.)

Your bar, which used to feel pretty intimate, has grown insanely popular over the past few years. It used to be just you and your friends who would go there, but now it seems everyone and their friends go there. In fact, your bar is now so popular that it's already done several major renovations and expansions and recently announced something that sounds pretty amazing: You and every regular will get your own massive chunk of wall space where you can hang up as many pictures and scrawl as many notes as you want -- and you can leave them up forever. (You wonder: How are they going to pay for all that real estate?) The bar is calling it your "Timeline" and encouraging you to make it sort of a "This Is Your Life"-style shrine to yourself.

You suspect it's soon going to take forever to move through the bar; to wander through all the Timelines of all your friends, you'd have to take a week off from work.

Also, they're adding a ton of free jukeboxes! That's in addition to the totally addictive video games they've got all over the place.

People keep saying that your bar is trying to get more "sponsors" and "partners," to help pay for all this stuff. You're used to a certain amount of advertising in the bar -- all those neon signs you've learned to ignore -- so you're basically accepting, while also a little wary. But the truth is , you mostly just come here to kick back and hang out with your friends -- to kill a little time and shoot the breeze. But whatever.

Occasionally you worry that you spend too much time -- way too much time -- at the bar. In fact, you feel a little bad about the other establishments you've stopped patronizing.

But, again, whatever. Drink up. Soak it all in. Have a good time. You could leave and go somewhere else, you suppose ... but hmmmmm -- now that you think of it, you're not even really sure how to get to other bars anymore. Are any of them even still in business?

Oh and there's something else about this place -- something sort of unsettling. All the bartenders here are total gossips and you have this vague sense that they're always talking about you behind your back. Mainly because they're always telling you things that you don't necessarily want to know about your friends. Do they really need to be all up in your business like that ?

The great Facebook 'engagement' land-grab

Citi analyst Mark Mahaney recently released some

rather astonishing data

showing that web-connected U.S. residents now spend about 16% of their total time online on Facebook. In the first quarter of last year, it was under 8%.

With that kind of growth in "engagement," marketers and media companies are constantly being told -- and telling themselves -- that they have to be on Facebook in a big way. But what does "being" on Facebook really mean? It's not just an existential question; it's a practical question, because Facebook, for all its talk about cozying up to brands and marketers, is still mainly a hangout -- a destination for friends who want to commune and waste mind-boggling amounts of time together.

The truth about social-media sites is that they've never been particularly great environments for advertising. People immerse themselves in social media because they want to socialize. (You wanna shop? Go to Amazon.) Bo Peabody, who launched one of the earliest social networks, Tripod, in 1995 (damn, remember Tripod?), once wrote about coming to this realization in a

Washington Post op-ed:

"By 1998, Tripod was the eighth-largest site on the web," he pointed out, but despite nearly a decade of hyper growth (it peaked in membership around 2001), Tripod ultimately couldn't cut it because of the pesky user-engagement vs. advertising-engagement problem intrinsic to social media. Peabody wrote that as millions of members poured into Tripod, he and advertisers assumed that all those warm bodies would amount to, well, an audience -- an audience receptive to advertising messages.

But not quite. "In one meeting with a top advertiser," Peabody recalled, "I was asked to pull up a random Tripod member page. What I got was a picture of someone's condom collection."

In other words, people want to do their own weird, idiosyncratic things (that are not advertiser-friendly or family-friendly) on social-networking sites. They're generally not looking to shop or bond with brands or otherwise serve as sponges for marketing messages.

Facebook has gotten around the social-media advertising-engagement problem somewhat by being much more ubiquitous than any other social-media product ever. Research firm Webtrends released

a report earlier this year

showing that click-through rates for Facebook ads are well below industry averages and actually fell from 2009 to 2010 -- but Facebook's advertising revenues continue to rise just because Facebook continues to grow and grow. In other words, advertising that 's subpar in performance can still potentially achieve scale not only because of how many people are on Facebook but how much time they spend on it.

Essentially, Facebook has to constantly battle against its very nature -- its supposed reason for existing -- as a friendly place for "friends" by conning those friends (and you) into "sharing" more and more, and by increasingly pulling intel about Facebook-linked activities (e.g., listening to music via Spotify, or reading an article off-site via a Facebook-linked app) into the picture of users it presents to marketers. It puts all of us to work (at $0 per hour) to increase its "engagement" scores because getting more and more people to spend more and more of their lives directly on Facebook -- or tethered to Facebook through an off-site app -- is the only way it can keep growing its advertising business and justify its valuation.

Meanwhile, as time spent on Facebook increases, media companies and marketers have fewer (and shorter) opportunities to engage consumers off-Facebook ... because there are still only 24 hours in the day.

But at what point does this "sticky" everything-and-the-kitchen-sink approach begin to backfire for the Social Network itself? As Facebook becomes sort of wallpaper for people -- the more it becomes a virtual web operating system -- does it really make them more eager to spend? Does sucking up higher and higher percentages of users' mindshare necessarily increase their responsiveness to advertising? Or, to the contrary, does it leave them feeling a bit numb, weary ... and used?

Your favorite bar starts to feel like a whole different sort of place when you realize that you're more of a hostage than a patron.

Simon Dumenco is the "Media Guy" media columnist for Advertising Age. You can follow him on Twitter @simondumenco.