It's under general preferences. The same as in previous versions of Poser.

Only in previous versions of Poser, your scale didn't affect materials. Whether you were you using feet or inches or meters or whatever, bumps were the same. Now, bumps are real-world scale, and maybe that's true of other material room settings, too. (Setting the Poser 6 scale to inches makes the bump settings from P4/5 about right, FWIW.)