I can try to give you an idea what the huge fuss is about (although the simple fact that it is a hug fuss should be enough)...
(1) I hate having to keep track of "which account" I'm dealing with - as far as I'm concerned, I'm me and Apple is Apple, and my ID is my connection to Apple and its services. Having to have two ID's and two passwords to be used in specific ways/settings is more than I want to have to think about.
(2) As an example of the potential complications, consider that I was trying to update 3 iOS devices and 3 Macs that I own to iOS 5 and updated OS X Lion. In the process of trying to follow the guided steps on my iPhone and MacBook, it sounded like I needed to use my MobileMe account to use iCloud so I entered that. Then it informs me that because I did that, I can't use my iTunes account on that device for 90 days to be able to use the auto update feature. If I could just correct it, it would be less severe, but now I feel like I have "one more thing to deal with" which is not what I'm looking for.
(3) There was a point in the past where I had an issue and went back and forth with Apple support to try to fix it and (a password reset problem as I recall) and it was all thoroughly complicated by the fact that I have two accounts (not my choice - was forced by having had iTunes then signing up for MobileMe).
These are just a few quick examples of why it's a pain. And it seems so unnecessary! I'm me! Let me have one account!