For those of you who may want to use older MF lenses with your D5100, or who like myself feel the D5100 has the focusing prowess of Mr. Magoo, I just got this info from third-party screen maker KatzEye:
"I am happy to report that the KatzEye screen for the Nikon D3100 model is fully compatible with the D5100 camera. We haven’t had a chance to update the website to reflect this information yet, but you may feel free to order the D3100 screen at any time."
