It's currently not possible to create a queryset which excludes models with given tags. I've fixed it with a simple patch but I'm not sure if it is the right way to do it.
if hasattr(value, 'prepare'):
if hasattr(value, '_prepare'):
to the get_prep_lookup method in TaggableManager after the first if block. Tested with Django 1.2.1
It's a little more complicated than that, I'm investigating though.
fixed in e1bbfa6
Thank you very much for this one. The library is an improvement over the django-tagging library. Keep up the good work!