Freshly ground coffee, how fresh should it be?
Coffee begins to lose its flavour and freshness as soon as the roasting procedure is complete. Whole beans are best used within a month of roasting. The best way at looking at ground coffee is that it is similar to the whole bean, only with a whole lot more (pardon the poor english) surface area. That means that any of the breakdown that occurs to the bean will occur exponentially faster with a grind. You should always grind beans for each use, if you wish to have maximum flavour.
I am no expert, but I can tell the difference between freshly ground beans (like my wife and I do), or not so freshly ground (like my in-laws do).  I am no scientist, but the older the grind, the 'flatter' the flavour. It is definitely noticeable.