This may be common knowledge to most of you but it was an issue I recently ran into and thought I'd share what I found out. I searched for a few hours with absolutely no luck on finding a solution so I figured I'd throw one out there in case anyone else has seen this issue.
On startup I began recieving a list of errors that looked like this and since I wasn't using python in maya at the time I ignored them...
'import site' failed; use -v for traceback
ImportError: No module named maya.app.python
ImportError: No module named maya.app.python
ImportError: No module named maya
ImportError: No module named maya.cmds
ImportError: No module named maya.utils
ImportError: No module named maya.mel
ImportError: No module named maya.app
ImportError: No module named maya.app.startup.gui
I assumed right off the bat it had something to do with my system/environment variables on my windows machine but wasn't sure which. If you have a version of Python installed already on your machine the variable PYTHONHOME may have been added. So where maya is using it's own version of python (I think it's 2.4?) my PYTHONHOME variable was saying to look in C:\Python25. I deleted this variable to remedy my problem and stuck the PYTHONPATH variable in my maya.env file.
Hope I didn't wast anyones time if they read all this and it's obvious but if not, hope it saves someone else some time.
-John