Re OS 10.6.8
Your "Downloads" folder in your user home area may hold some surprises: Downloads you couldn't find, or forgot about. Apps or updates files no longer needed but taking up disk space.
This folder is separate from the "Mail Downloads" folder, which may also have stuff you don't need anymore, or that "lost" copy of something.
Look at them both from time to time. I put them both in the finder window sidebar because it's easy to forget about them.
"For what is age but youth's full bloom,
A riper, more transcendent youth" - Oliver Wendell Holmes
Thanks for the good idea about putting them in the sidebar.