I 'know' that freshly ground coffee is the best there is (within the quality of the beans, that is).  The question is whether this is true. Freshly ground coffee smells great, but does that affect the flavor after brewing? How long do these volatile flavors or smells last before the coffee goes 'stale'.  Can anybody (experts) taste the difference between freshly ground and brewed or not so freshly ground coffee? If so, what differences can be observed?  Edit as per talon8's link:   Freshly ground: brighter acidity, richest flavor. 9 hours: very similar to the freshly-ground coffee, although a bit mellower; less “bright” notes. 24 hours: some of the fruity flavors have faded; a bit less flavor in general. 7 days: duller, significantly less flavor overall.   To the people that notice the difference in taste, do you agree with these observations? 
Posted as answer by request of @BaffledCook:  Here's an slightly informal blog post outlining changes in taste between varying degrees of freshness in the grind of a coffee.  http://investigationsblog.wordpress.com/2010/03/03/do-i-really-have-to-grind-coffee-right-before-brewing-it/  The short version is that the coffee starts losing freshness as soon as it is ROASTED. The longer it sits the faster it goes stale. The more surface area it has (ie: you've ground it up; also, the finer the grind), the faster it goes stale. The more you expose it to air, the faster it goes stale. So, seal your coffee in an air tight container at room temperature. And grind as close to the time you add water to it as possible.  How much of a difference detected depends on the the actual coffee been, the roast, the taster's taste buds. If you buy a bean that's been sitting on the shelf for 3 months already, you will probably notice less of a difference than a bean that was roasted last week. I buy beans that are roasted and sold within a week, and I DO notice a difference if I leave the grounds for a day or two before drinking. 