If you empty your trash in Snow Leopard and it seems to be taking forever and using a lot of CPU, it's probably because Snow Leopard does a secure emptying of the trash by default. With the secure emptying, it increases security. But it does take a long time. If you want your trash to get emptied quicker, you can turn this off by opening the Finder and going to "Preferences..." in the menu. Once the preferences are open select the "Advanced" tab and then uncheck the box next to "Empty Trash securely".

I've also heard people say that unchecking this box and then turning it back on results in secure trash emptying that is quicker. This didn't seem to work for me. But might be worth a shot if you are looking to speed things up.