Would you consider buying a domain name through Google for your blogspot's blog? Since all my links are pointing at my blogs at blogspot.com, I wonder what is the effect of shifting the blogs to paid domain through Google. I hate to think of changing the profile information in so many places.
You can't go wrong with a custom domain name. It's just more professional. However, I can't speak from experience regarding buying one through Google. I do all of my domain business with Namecheap. If you are worried with pagerank and the like, it's probably best to research that a little...or start building some with a new domain. If you do decide to buy a domain, do it for the long haul, so you only have to change your profiles once. You can purchase domains in different increments, the lowest is one year. So, the worst case scenario is, you have to change your profiles again in a year because you let your domain go. Best of luck!