Yep. I am in this situation too. It's absolutely brutal.
I've been slowly turning on more iCloud services, but am in a weird state where my media and purchases use my "preferred" iCloud account (name@gmail.com), while all of the other native iCloud services use my name@me.com account... which I can't figure out how to change to name@gamil.com.
I'm surprised there aren't more people who are in this situation. I got into this mess because Mobile Me required me to have a different account than my iTunes account (name@me.com), and then that eventually became iCloud, while app purchases and everything else stayed with my iTunes account.
I'd love to merge them, and I have absolutely no idea how to. I don't even think this guide that you linked to helps me much, to be honest. I'd be too afraid to lose something.