Anyone notice Canada's current account balance went from being an almost $7 billion quarterly surplus to going in to a $500 million deficit in just two quarters ? $23.6 Billion surplus in 2006, $14.2 Billion surplus in 2007 and starting 2008 in the negative. That is what happens to the Canadian economy with a high dollar. If Canada isn't cheap...the world doesn't buy it's stuff, its services or visit the place. Yes we got a billion dollar increase in energy exports from higher ($US) prices, but that only makes up for the $1 billion we lost in auto sector exports. Then start subtracting the exports in goods, services, nickel, forestry and other sectors...and wow.
Fundamentals do not support prices of wheat, gold, oil and others. That doesn't mean they have to trade on fundamentals all the time...but eventually they will fall back to earth.

Commodities have always and will always go through boom/bust cycles. Anyone care to say "it's different this time" ?

That being said...I fully expect commodities to keep going up for a while. It's just that I have no idea how long a while is. Bubbles can last for years.