Currently, there's no way to get a list of what files were installed (full paths preferred, since the person running rpm may relocate the package in many cases) from a %pre or %post, and ditto for files removed in a %preun %postun. This information would often be extremely useful to have.
rpm-4.1 permits concurrent access to the rpm database, so the list of files can be gleaned by doing, say, %post FILES="`rpm -ql %{name}-%{version}-%{release}`" ... Watch out for multiply installed pacakges however ...