This is a question I've always wondered so now I'm going to ask.
When you install Redhat Linux on a dually rig, it installs a kernel for SMP and one of non-SMP. (I suppose other distros may do this to, I just haven't installed them.) Both kernels are installed in the boot loader with the SMP as the default. My question is: why would you NOT want to run a dually with an SMP kernel?