I used Homebrew to install libjpeg and PIL and got the following error:

$ python -c "import _imaging"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: dlopen(/usr/local/Cellar/python/2.7.1/ \
    lib/python2.7/site-packages/PIL/_imaging.so, 2): Library not loaded: \
Referenced from: /usr/local/Cellar/python/2.7.1/ \
Reason: Incompatible library version: _imaging.so requires \
    version 12.0.0 or later, but libjpeg.8.dylib provides version 9.0.0

It seems that libjpeg 8c is not compatible with PIL 1.1.7. To fix this I rolled back the libjpeg formula so it [installs 8b][4].

[4]: https://github.com/mxcl/homebrew/commit/bf24002de7537003e4757025b75709f6aea03a01#Library/Formula/jpeg.rb