Sooner or later, you will consider the idea of buying your own domain name. If you are obsessed (this is too strong a word, I know, but I always like to exaggerate things) with your Google and Alexa rankings, I suggest that you do it early. Buy your own domain name while you still haven't reached a Google Page Rank of 3/10. Why? Domain age is one area that's considered when evaluating a site. The older your site is, the higher its importance in the World Wide Web -- or so I "heard" from other bloggers. The moment you register your own domain name, your site's age returns to 0 (zero) and you lose everything like Facebook Likes, Google PR, Alexa Traffic Rank, and backlinks; hence, it's good to do it early and to do it right.
Before you make that very important decision, look around and compare the prices available on the web. Do a Google or a Yahoo search and you will see that prices of domain names range from $1.99/year to $10/year. I'm not promoting any particular webhost here, but I just want to tell you that there are sites that sell domain names at $1.99. I didn't know this at the time I registered mine. Good luck!