So far so good. I did a clone of my drive with SuperDuper, booted from it to ensure it was working, then did an “archive & install” of Leopard. Other than a few programs needing updating, a few Mail add-ons getting broken (which I expected) everything has gone smoothly and all my programs seem to be working well. Shutting down is really fast with the new OS, while booting up doesn’t seem as fast as I might have expected. Some programs definitely open faster, other’s don’t seem to be all that effected (Pages seems rather slow to open, which surprises me).
A few quibbles with how Leopard handles my Airport Extreme shared drives, and I’ll probably be tweaking the dock, but overall things seem good with the new install.