There is an interesting article on the back page of the latest issue of APS news about using the GRE exam as part of the admission criteria for physics graduate programs. It’s also available on-line here: http://www.aps.org/publications/apsnews/201302/backpage.cfm

Here is a short excerpt:

Of these [physics grad programs], none … have concluded the GRE predicts success in research …. Our analysis finds that the QGRE correlates with only one metric, the graduate GPA (but it is such a weak correlation the scientist in me rebels when fitting it to a line). That said, we find undergraduate GPA to be a better predictor of graduate GPA.