Just read a great article over at Lifehacker, Set Up a Self-Cleaning Mac with Hazel. If you want to be able to set up your Mac so files you download automatically go to certain folder, or even be automatically imported into iTunes or iPhoto, check out Hazel and the how-to article. Oh yah, another feature I really like is the Trash management. You can set Hazel to automatically remove from the Trash files that are, let's say, over a week old. You can also set a maximum size for the Trash (and how over-sized files are handled).