Hello,
Google Chrome users may have some problems with the Downloads stack, as the latter doesn't update correctly when a file is finished downloading.
My friend Hubert Sainte-Force provides a fix with explainations both for Hazel and Automator : http://steforce.oin.name/read/google_chrome_and_stacks.
(PS: Administrators, let me know if you prefer me to write a complete tutorial instead of a quick link)
Regards,
join