You can get an idea about some of the principles of variation by taking a look at everyone's favorite topic, corn prices. If you examine the average national corn price for the last ten years you will find that it was $2.28/bu with a standard deviation of about $0.43. Just by looking at those two numbers you can get an idea that there is some considerable variation going on in the historical pattern of corn prices.
Calculating the coefficient of variation (CV) yields 0.189, which you will recall is the standard deviation divided by the mean. Now if I were to ask you if the volatility in the corn market had increased since October 2006 what would your gut reaction be? I suspect you would be suckered in to saying "yes".
Let's take a look. The average price between October 1, 2006 and the middle of June of 2007 was $3.54 with a standard deviation of about $0.33. So in these short months, the price has risen dramatically compared to the last ten year average (an underlying structural change: read non-market subsidy for gasohol). So it is safe to say that we are not looking at an extreme value from the previous distribution, we have a new distribution of prices. (Unless of course you want to argue the really really long run approach to these things). So as you see, the interpretation of these things depends on your time frame.
Note however that the mean increased and the standard deviation decreased compared to the ten year average. This is because going up does not volatility make. Volatililty means up and down. Going up and staying there is not a risk increasing event (except on the rising portion, but then again, that didn't take very long!).
So we see the CV for the last several months (arguably not a fair comparison to the last 10 years) is about 0.093 or roughly half the relative variability of the last 10 years. Well stay tuned, I'm sure corn prices will create a much richer distribution for you over time with all the volatility you would ever want to face but so far, it has been up and relatively flat.
