A very small revision is required to make PyWordnet compatible with WordNet 3.0.
First make sure that WNHOME is actually specified on your path even if you have done a default install of WN 3.0.
I edited wordnet.py, and changed line 52-56 to have the correct path for your system. For example, I changed
line 56 to read
on a Mac OSX.
This worked very well.