I don't have a Facebook account.  To date, I never have had a Facebook account.  I hope I never do have a Facebook account.

It can be difficult to justify not having a Facebook account in this socially connected world where the majority of the people I meet now have Facebook accounts.

I originally didn't have a Facebook account because I already had a website on the Internet where I could share what I want to share.

Then later I didn't have a Facebook account because I didn't really need to have a Facebook account to connect with anyone.

Now, I don't have a Facebook account because Facebook's reputation, especially around privacy, is headed for the toilet (while its user base continues to grow).  Here's one of the best snapshots of the Facebook privacy issues I've seen in one, relatively short, place:

http://www.eff.org/deeplinks/2010/04/facebook-timeline/

Thanks to Steve Bohlen for the link.