Great, sage advice from John Scalzi about why a writer might want to pay to register a domain in the era of Facebook:
So, let's go back to 1998. You're a new writer and you want to establish a permanent residency online. Which would be wiser: Having your own site at your own domain, or putting up a site at GeoCities?
It's 2001, same drill: Which is wiser: Having your own domain, or creating a site on AOL servers?
2003: Your own domain, or a Friendster page?
2007: Your own domain, or a MySpace page?
(Hindsight is a useful thing.)
And now it's 2011 and the choice is one's own domain or a page on Facebook. Guess which I think you should do.
I agree with everything he says right up to the point where he recommends getting a Facebook page too. Not because it might not be good for your career, but because I think it's an ugly, stupid service designed to teach you to systematically undervalue your privacy.