As of June, 2004, SMP (Symmetric MultiProcessor) support has been merged into the main OpenBSD development branch. At this time, the i386, amd64, mvme88k, sparc64 and macppc platforms supports SMP, but hopefully others, including sgi and sparc will ultimately support SMP.
Please see the appropriate platform page for SMP status for your system.
We plan to put up links to good documents here whenever we find them: