well its not leopard in general...its the type of machine you run leopard on. i have a dual 2.7 G5 and that is supposed to work fast with everything lol, but i installed leopard and i had nothing but problems. so i went back to tiger and it works fine.
i installed leopard on my Macbook Pro (intel based) and everything runs smooth. the problem doesnt lie in the software, apple was just too lazy to try and correct the problems with leopard and machines that came out before 2006. so if you are using G5 powerpc systems or earier, you will have many problems when it comes to video and film.
on another note, if you plan on using leopard and maya...that just doesnt work at all lol