Apple ID - Want to make my xxx@icloud.com primary Apple ID? I recently created an @icloud.com address and now I would like to make that my default or primary address for my Apple ID instead of my current @gmail.com address. 

I tried to change it through the Manage Apple ID page but it said 'Not use a domain used by Apple'. 

Is it advisable to change my Apple ID from @gmail.com to @icloud.com?
This problem still exists to this day.  When you set up your Apple ID you are required to enter an already in-use email account that is not associated with an Apple domain.  This becomes your primary Apple ID email account.  From here you can then set up your @icloud.com account but you cannot set that @icloud.com address as the primary account address because Apple does not allow users to do so with Apple owned domains. 

Not to be confusing, but you can set the @icloud.com address as your Apple ID.  To do so, just attempt to log into your primary email address a few times until you are prompted to go to iforgot dot apple.com.  From here just enter your @icloud.com address and select to verify account by answering security questions; do not use verify by email.  Once you successfully answer the security questions you will be prompted for a new password.  After that your @icloud.com address will become your default Apple ID, you can now access iCloud with the @icloud.com address, and you can now use the @iclould.com address for email.