To "prove" his argument that commodity prices and inflation have no relationship, Krugman has a blog post in which he uses the graph below.
The problem is this: Which commodities? We have seen prices of gold skyrocket, although Krugman would regard gold as passe or even evil. But an even more important bellwether would be oil prices, since oil worldwide is denominated in U.S. Dollars. Thus, oil might well be more sensitive to changes in the value of the dollar than might other commodities.
In other words, de-homogenization might be something worthwhile here. Just a thought.
The second problem I see is that once again, Krugman uses the deus ex machina explanation of "volatility" to explain away anything that might be uncomfortable. Are oil and gold prices going up? Well, so what? They are volatile; that explains everything.