Apple notes that “MacBook Pro 3,1 is not supported in this build of Mountain Lion. Future developer previews will restore support for this configuration,” Gurman reports. “You will need to have build 12A178q or higher installed in order to see the update. Once the update is complete, your system will be at build 12A206j.”
Read more in the full article here.
[Thanks to MacDailyNews Reader "Dan K." for the heads up.]