When I take on a new client, the first thing I get them to agree too, is the creation of a new Gmail Account that will be used for everything related to their Wordpress Website. I then use this mailbox to setup their Google Webmaster Tools, Google Analytics, Wordpress.com Account (Akismet etc).

When I hand over the website, I hand over the Gmail Account; This ensures separate API Keys, frees the client up from doing stuff he/she doesn't want to do and in the end gives them complete freedom to do with the accounts as they please once my job is done (assuming they don't want me to continue with site maintenance etc)