I keep my Public Drop Box folder and a Samba share online all the time when I'm on the college network, and occasionally someone will drop files into either. Sometimes I won't notice for a while afterwards, which is annoying if it's big or I need to organise the folder better. So I wrote this Folder Action AppleScript that pops up a Growl notification whenever a file is added to a folder.
Just add the script as a Folder Action on a folder that you want monitored, and it'll pop up whenever something is added. If one file is added, the icon of that file pops up in the Growl notification; if more than one are added, then that folder's icon is displayed.
[robg adds: I haven't tested this one.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060515090933747