If you decide to host with a domain registrar (or decide to have your hosting provider purchase your domain for you), read the TOS first. Find out what happens if/when you decide to cancel hosting: will you retain rights to the domain, or will the host retain those rights? If you go with a registrar, and decide to host your site somewhere else after a certain period, will they lock you out of updating your domain details?
I've heard lots of stories of how people wanted to move to a new host, but their old host wouldn't let them take the domain with them (not just the 'stories around the hosting forums', but friends of mine who've lost sites into which they put years of work). This can be a real hassle, even if you only have the web site set up to house your personal blog which doesn't get much traffic.