Yeah, there are many factors. The many college textbooks on a shelf can be forgiven if there are many, many other shelves in the house. The shelves that only contain bestsellers or Oprah's bookclub books make me sad. And then I get even snootier and see if the person has genre shelves. That isn't even enough! I have to make sure that they're reading genre written by women, as opposed to the standard Heinlein/Asimov/Clarke stuff.

I need to start keeping books in my car as "just in case" insurance.