Only improvement I've found with Snow Leopard for my uses is it's slightly faster than Leopard. However some other things annoy me. Behaviour of some desktop apps (Dock apps) has changed for the worse. Repairing permissions in safe boot takes forever. Some other 3rd party programs do not behave well in Snow Leopard; eg: I've had to force reboot the computer because the program would not properly force quit (interface still visible even though the app had disappeared from the active programs list.)

I'd need to do some more testing of the firewall to find out more.