I'm one of about twelve people in the world who doesn't have a Facebook profile -- or whatever they're called.
1) I've heard anecdotal (e.g on news programs) instances of people closing out their Facebook account, only to find that after a while it gets re-activated for you. Also that even when you close out your account, all your data is retained.
2) My understanding (and limited experience) is that one can not view another person's Facebook page unless you have a Facebook acount. This is in contrast to (most) blogs, corporate/organizational/individual websites, MySpace, and others. I can accept not being able to post **comments** unless one is a member, or if it's a service to which one subscribes -- but to not even be able to **view** a page unless one is a member seems exclusionary, and a bit "precious" (an Aussie term). So, "Thbbbbtttt!!!" to Facebook. (Addendum: I've been informed that this isn't always true. OK -- fair enough.)
3) According to Wil Wheaton's blog, Facebook has an ongoing habit of (a) steamrolling over privacy issues, (b) exercising poor data security, and (c) activating "features" on accounts, thereby forcing people to opt **out** (as opposed to Blogspot/Gmail, which tends to hound you about new features, but generally has an "opt in" approach). No thanks; not the sort of people I like to interact with.
4) That facial recognition stuff is freaky. Although it's the new reality, so in a few years it'll be unavoidable.
5) I don't feel the need. Everyone I really need to communicate with online, I do through e-mail.
6) I really don't need yet another username and account. I have too many online accounts/usernames/passwords as it is.
7) I arguably spend too much time online (granted, mostly in pointless Google searches, Wikipedia links, and YouTube ''trails''...). I don't need to open another black hole (and part of why I haven't signed up for Twitter; I've also pared back on the number of blogs I follow).
8) Fear of identity theft. I use a pseudonym here on my blog, as well as code names for family and friends. I don't feel like ''going public'' with my name, to aid people in figuring out my identifying particulars. And if I continue my pseudonym on Bookface -- well, what's the point, then?
I think that's it; there may be more, if I thought about it. ;)