I have a Google Profile at the easy-to-remember URL http://www.google.com/profiles/109794546034821268026. Why not /davextreme? Because that address is taken. By me. And I can’t merge my two Google Accounts together. Trying to add “davextreme” to my current Google Profile, I get the message “You can not associate a Gmail address with your Google Account”.
See also, the harrowing “Fixing the Google Account problem”.