Things I'd like to add. Assuming these are actually possible.
%autosetup for EL6 and 5
%_smp_ncpus_max for EL5
python2 macros for EL6 and EL5
%install buildroot cleaning in EL5
%clean section in EL5
Tack this onto %files?
BuildRoot: definition in EL5
Not sure this is possible. Maybe tack it onto %files as well?
%__global_ldflags in EL6 (and maybe EL5)
Requires redefinition of %cmake, %cmake_kde4, %qmake_qt4 and %configure
%make_build for EL6 and EL5