I deleted my Facebook account a couple months ago and havn't regretted it yet!
From what I've heard, you can never truly delete Facebook. If you ever want to back to the site, which a lot of people do, it's a click or two away.
They keep all your information. Even information that you don't know they have. There was news story about some guy over in Ireland who had Facebook Subpoena'd for invasion of privacy. When Facebook coughed up all the info they had on him, it was scary the sheer amount of personal information they had on him.
Remember, facebook doesn't end at Facebook.com. The site embeds "Super cookies" in your browser that record all your web surfing behavior. Besides that, with the rollout of "Timeline" Facebook is making a shameless grab at your personal information
before Facebook existed.
What kind of diapers did your mom buy for you? They'll find that out somehow, and sell this info to advertisers, so you'll buy the same diapers for your kids.
Facebook is constantly gathering your personal information. And selling it. Make no mistake.
It doesn't surprise me that they are the #1 most hated company. But as Destin says, everyone is there, so it's an easy way to keep in touch.