You might try the solution I posted in this topic: TS3998 All my contacts have disappeared from icloud and all my devices\. It's all theory until the OP tries it and lets us know if it's a valid solution.
But before you log out of iCloud make a copy of the AddressBook folder in your Home/Library/Application Support folder.
Thanks. I ended up spending several hours at the Genius Bar, and we figured out that it was caused by a multitude of issues - one of which was corrupt user preferences. I had to delete my user account (Mac OS user account, that is) and reconfigure email etc on my laptop. Now, everything is working. Thank goodness for backups!