This whole Multiple id, iCloud, iTunes acct thing should not be as big a problem for most people as I usually see it made out to be.
I've been using all these services for a while now and I haven't come across a problem, besides the inconvenience of having multiple ids/passwords.
The only way i could see this being a problem is if you have multiple purchases on multiple accts. iOS 5 allows you to be signed into different accounts for different things.
I personally have two id's a MM acct and and iTunes acct. I had the iTunes acct first and used it for all of my purchases. Then i got a mm account and used it for mail and sync and whatnot. Now with iCloud I moved my MM acct to iCloud. so thats the acct i sign into iCloud with on my phone. For the iTunes store i am still signed into my original iTunes acct with my purchases(apps,music) for iTunes match i signed up with my iTunes acct.
All of this stuff works flawlessly and i have not had a problem. If i buy a new app I use my OG iTunes acct pw. When i login to iCloud, in the browser, on my phone, etc i use the mm acct that moved I to iCloud. iTunes in my computer is logged into my iTunes acct. Again this setup has been working flawlessly for months and i've had no problems. Hope this helps. Reply if you have a question.
Thanks for the explanation. I just want to clarify a bit. I'm in the exact same situation as you. At first I only had a GMail addy Apple ID for purchases. Then I had to create a new @me.com email for MobileMe. I plan on moving my @me.com MobileMe to iCloud for my contacts, calendar, and mail. So then I'll also be able to tie my other GMail Apple ID to it too as a secondary email? how does this work?
When I log into iCloud, I expect to use my old MobileMe log in. Is this correct?
However, when I make app purchases, will I have to use my old gmail Apple ID?
I'll have to remember to use different email and pw for each one?