Many people recommend leaving items in the Trash — as it often happens that one later realizes that a deleted item is actually needed. I have a habit, however, (possibly due to a subconscious concern of letting things get out of hand) of emptying the Trash on my MacOS X system almost as soon as I place something inside. Compost is a utility (implemented as a Preference Pane) that will monitor the items in the Trash, deleting files that are older than a specified number of days. In addition, it will limit the total size of the trash to a configured size. With Compost watching over things, I can safely Trash items, knowing that I’ve got a month of margin after which they’ll disappear.
Compost for MacOS X