Could not login into Facetime and Message 10.8.2
A possible solution is to change your DNS server settings. 

I had this problems for a while, and a friend too, and the solution that worked for us was just changing the DNS servers to Google's DNS.

To do this, go to System Preferences > Network > Advanced > DNS >

Then press the + button on the left below DNS Servers, and add both: 

8.8.8.8 

and 

8.8.4.4

Hope this helps!