Is a me.com address only used for email in iCloud (outside of brand new accounts)? I am one of those people who had an iTunes account way before having an .mac or MobileMe account. Since one can't really merge accounts, I have been trying to decide what to do about my iCloud account. 

According to Apple's documentation, their recommended setup is to upgrade your me.com account to iCloud, and then just use your iTunes account for purchases and iTunes in the cloud. 

I am debating on actually NOT fully migrating my MobileMe account to iCloud, and instead upgrading my iTunes account to the iCloud account.

My question is this - if I upgrade say my gmail.com account to iCloud, and sign up for a new me.com address - is that address ONLY used for email? 

For example, if my wife wants to share a calendar with me, she would use my iCloud account (which would be my gmail account), rather than my new me.com email address?
Yes, it is only used for email. My Apple ID is an old .mac username which wasn't associated with a MobileMe account. It allowed me to set up iCloud using only that account name. When I turned on iCloud email, it prompted me to set up a new @me.com email address, which I did. But I still use my .mac username to log into icloud.com and access the iTunes store. The new email is only used to send and receive emails.