Many people have been asking about the new “My Client Center” since a member of DigitalPoint reported seeing in his account when he logged in last night.
This is actually one of the many limited release or invitation-only beta tests that AdSense runs. So you likely won’t be seeing the client center in your own AdSense accounts. According to the thread, it does appear to be linked to the AdWords Client Center, as Sem-Advance did reveal he is also part of that program.
So rest assured, I have confirmed this is legitimate, but it is simply a limited beta test at this time.