Hazel's rules function a lot like Mail.app's and other rule-based systems, so most users should feel right at home. The beauty here is in the sheer power available in building workflows like this, and Paul Kim, Hazel's developer, has posted a Tips & Tricks section at Hazel's site to offer some ideas, and he also includes a set of sample rules for importing to help you hit the ground running (none of the rules are enabled by default after import, so your files won't get, uh, filed until you say so). Imagine: being able to have Mac OS X automatically delete unfinished downloads after a specified number of days, or automatically assign a label and move a document or other type of file to the Desktop after you haven't touched it for a week.
Hazel's potential for bringing an entirely new level of organization to your workflow is refreshingly endless, and I'm genuinely excited for the potential of this app. This 1.0.1 release is a Universal Binary, and Paul has even incorporated an interesting way of offering three different registration modes for Hazel: evaluation, demo and registered. Registered is, of course, when you purchase a license for a mere $16. The evaluation period allows Hazel to run feature-full for 14 days after installation (except for exporting rules). Hazel steps down to demo mode after that 14 day period, allowing you to run up to two rules on one directory at any given time. Not bad for such a potentially useful app, so take it for a spin.