I had not thought of (until now) whether such a script would be interesting for the general public, but after I saw the script of zOffTy, I decided to upload my version too.
The version of zOffTy is nice too. It operate on selected faces. My version use my custom "smart selection" that I found as good time saver, especially for poly objects with many faces. Check both versions (zOffTy Average Normals & my Poly Average Normals) and have fun ;-)