When pass-by-pointer is preferred to pass-by-reference in C++?

Question

I can imagine one case, in which the input parameter could be NULL so that pass-by-pointer is preferred but not pass-by-reference?

Can anybody add more cases?

Answer 1

Google seems to have a strong opinion on this, and I tend to agree:

http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml#Reference_Arguments