I have learned the hard way that Python Extensions such as NumPy and PIL are incompatible with Maya 2013 unless they are recompiled against Visual Studio 2010.
Apparently Autodesk compiled Python 2.6 for Maya 2013 against VS 2010, where Python 2.6 and extensions for 2.6 are compiled against VS 2008.
http://grokbase.com/p/python/image-sig/118js6g1e3/help-with-pil-on-64-bit-windows-7-and-maya
