Personally, I like setting up a 'shell' account to be the primary login (remember, this will be the prime Google account you'll be logged into when you visit other services like gmail, froogle, etc), and then linking all the other accounts under this one.
As far as I know, an MCC account IS a "shell account". It's only purpose is for managing other accounts. You can't even create campaigns directly in an MCC account, right?
I'm a bit confused about the "converting into an MCC" comment, as well. I thought you just signed-up for an MCC, and then you have... well, an MCC. Is this related to the "Google Account" issue? I did notice that as soon as I created my MCC, I had to convert the login to a Google Account. Seems kind of silly. Why don't they just create it as a Google Account in the first place.
I sure find it confusing. I have three Google logins - one for an MCC and two for Adwords accounts. When I actually DO log-in to Google for more generalized services (or to post on Google Groups) there's no telling which ID I'll be logged into. If I'm already using one of the accounts, then I have no choice to log in to a different one, because that would end my session with Adwords. So, I have three different IDs I post under on Google Groups!
As far as being logged into a variety of Google services - agree that its very annoying that there isn't more control over this. Google has pretty much forced me to not use their start page, gmail, etc as I can't stay logged into an MCC and a second account at the same time in the same browser (if you open IE, Firefox, Opera, etc - you can stay logged into different G accounts at the same time within that browser).
If you only have a few Google accounts, then you can use their access feature to enable other Google accounts to access them - but once you have several MCCs, Analytics, Froogle, et accts - its just not worth the time to keep them all straight anymore.
I'd really like to see an interface to manage all my Google accounts and premissions from a single place.