The common wisdom I've heard is that dried herbs and spices:

* have a shelf-life of about a year or 2
* keep best in a cool dark place
* will release more flavor when crushed

That's fine but some spices are expensive. We have over different 50 jars on our spice rack and can't afford to replace them annually. Also, it's hard to believe that all herbs and spices are created equal.

What are some more specific guidelines regarding the shelf-life of herbs and spices? Which last longer? Which last less long? How much is shelf-life really affected by light or lack thereof? Do any actually become health hazards if left too long?