User CP?
Its the User Control Panel, Mike. (where you change avatar and profile info)
I think the button for "User_CP" is missing form the array here, most forums its up with the Home | Help | Search |
But the only way iv found to access it is clicking on the message link at the very top of the page "you have 0 messages"
Then it will give you Arduino Forum ? User CP ? Inbox, so you just click on User CP. 
or click on http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?action=mycenter if you are logged in.