Does anyone have any tips on repairing posterized areas of a photograph, without resorting to some plug-in? Should I just blur the whole image and paint the blurred, posterized areas back in with the History Brush?

Hi there, Ray. Welcome to RetouchPRO :bigthmb:

It's a bit difficult to give good advice without a specific image as an example.
But, yes often a controlled blur is on oneof the answers.

A tip though..... A blur can help on the solid parts but will ruin the edges. For the edges use the Noise>Median filter.

Rô