One important aspect of corporate reputation is what it's like to work there-- and this is important on the department level and smaller level.

Abusive work environments cause a tremendous amount of misery, and there's no reliable method of finding out whether a job is likely to land you in one.

This problem is made worse if leaving a job makes an potential employee seem less reliable.

Another aspect of a universal reputation system is that there needs to be some method of updating and verification. Credit agencies are especially notable for being sloppy.