If you already have a .me and/or the older .mac account, you can continue to keep using those addresses or even use the .cloud as all three actually go to the same email account.
It may however, take a few weeks for the .icloud.com address to show up in your account. Mine hasn’t yet. I believe that if you never had one of the .me or .mac address you will be able to use those with your new .icloud address.
See the full details at: http://support.apple.com/kb/HT5441?viewlocale=en_US&locale=en_US