Facebook knows what it's doing. Everything about the way it runs indicates the geniuses behind its crisp interface know exactly how to draw you in, and keep you in. Applications, games, pictures, videos, news links, friends, messages, event invitations, photo tagging, commenting, quizzes ... it's one big party at an arcade with every single person you've ever cared enough about to hit "approve" when they request you as a "friend." And you can join in from almost anywhere at any time. You just need a cell phone (or a laptop or an iTouch or a Blackberry ...).

Facebook also knows how exhausting it can be, and that its users need distance sometimes, which is why its "deactivation" feature is brilliant. When the Facebook-weary decide to stop using, they have the easy-to-commit-to option of deactivating, which just suspends the account. You'll stop receiving e-mails when someone tags you in a photo, your profile evaporates and you no longer exist on Facebook. But if the time comes you change your mind and you want to come back, you just reactivate and everything is fully restored and back to normal. This makes "leaving" Facebook a low-risk feel-good accomplishment.

You can find many, many blog posts about Facebook de/reactivation, and they sound a lot like testimonials from failed dieters. One Blogspot blogger, "Rebel Mel," writes (ellipses hers), "So, uhm, I guess what I am trying to say is.. uhhh. I um, reactivated my facebook account. I don't know why. One second I was psyched that I had broken away from that lame site.. actually about seven months I was free from it. ... I kind of wish that I hadn't. Maybe I will delete it, again. Who knows."

The Internet plays a crucial role in our day-to-day routines at work, paying bills, Googling maps, reading news, watching TV, networking socially. The line seems pretty blurry between "addiction" and "general use." So hours and hours spent on Facebook might just as easily be recreational as they might be irresponsible. Either way, people tend to express Facebook remorse. They get sick of clicking endlessly through photos of people they don't know or shouldn't care about or taking quizzes to see which dead movie star they most closely resemble. In fact, even Bill Gates was reported to have left Facebook. Last month, Gates is quoted on Yahoo! Tech, saying Facebook "was just too much trouble, so I gave it up." Gates said about 10,000 people wanted to be his friend. He couldn't take it, so he bailed.

Dr. David Greenfield, head and founder of The Center for Internet and Technology Addiction, based in West Hartford, has been warning people about the dangers of Internet addiction since the mid '90s.

"The whole Internet operates on a variable ratio reinforcement schedule. What that means is there are rewards that come online, for example, in the form of an e-mail you were looking forward to juxtaposed against a lot of junk mail," he said in a recent phone interview. You get a pleasant feeling when that e-mail arrives, and you look forward to the next one.

"It's like a slot machine. Every once in a while you get this 'reward': E-mail. But you don't know how many you're going to get and you don't know when. The Internet functions that way," Greenfield said.

So when your Facebook homepage updates, prompting you to click "show new posts," it's a little like getting a little high or winning a few coins, etc.

I also spoke with Marion Stansbury, who's a marriage and family therapist. She works with Internet addiction, but more of the cyber-sex/porn sort, and online relationships.

When people are unhappy in their relationships, they take comfort in connecting with people through Facebook, whether with people from their pasts or people they don't know, Stansbury said. "That takes energy out of the relationship. What I do is I help my clients to put some constraints and limits on some of their excessive behaviors," she said.

Greenfield and Stansbury both said their Internet-addiction patients primarily have complications with porn or gambling and Greenfield said parents from all over the country fly their video-game-addicted kids to his office for treatment.

"One of the hallmark features of Internet addiction or addiction of any kind is the desire to stop, attempts to stop and the inability to stop," Greenfield said.

Looks like re/deactivators like "Rebel Mel" might be in the development stages of addiction. However, Greenfield said he hasn't seen too many certifiable Facebook junkies. But how are we supposed to know when too much is too much?

"If it's not interfering with your life in some way, then what's the issue?" he said.

That's a complicated question. According to Yahoo! Tech, Bill Gates himself, pressed further about his Facebook departure, said, "All these tools of tech waste our time if we're not careful."