Perhaps I'm reading the "leopard incompatibilites" thread without enough grains of salt. It seems awfully bad looking at that thread.
I removed APE (a third party-extension KNOWN for causing problems) prior to upgrading to Leopard. I ran an upgrade, and the ONLY problem I've had so far is I had to update to the latest version of Parallels before it would run. All my other software? The entire upgrade has been seamless. The incompatibilities are overblown.
Have you seen the sheer amount of incompatibilities with Vista?!?