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