The cause of Leopard crashing is Application Enhancer, a toolkit that gets (silently) installed with this and other software. The problem is that it modifies the OS in ways that is not supported , which has caused lots of incompatibility problems when Leopard came out and is even a security hole . Even Apple recommends removing it in their support docs if you have trouble.

Personally I would stay far away from this and any other applications that use AE. At least people should uninstall AE before upgrading to Leopard to avoid problems.