While the WGC says inflation risks are still the strongest fundamental on gold prices, central bank policy and gold purchases are a growing force on price direction.

Despite fewer purchases overall, demand is still historically high, paced by central banks stuffing reserves with the yellow metal.

Natural gas. No other commodity is the subject of more hand-wringing. But while the resource has been investor kryptonite, there may be a silver lining in all the consternation and a real opportunity for savvy ETF investors with cast-iron stomachs.

Despite a decline in gold demand of 5 percent in the first quarter, the World Gold Council says central-bank buying here to stay, changes statistical report to reflect it.

If you've watched the roller coaster of gold prices, you might be a bit queasy. And if that upset stomach made you think about returning to the world of equities through gold miners, you wouldn't be alone. Precious metals mining ETFs now hold $12.4 billion in AUM. But what exactly are you getting with this not-quite-gold exposure?

World Gold Council’s quarterly report shows how price can influence demand patterns.

Oil. It’s a finite resource and we’re running out of it. Unlike shares of Microsoft or ears of corn, there is only so much to go around. In theory, this long-term supply constraint is one of the few sure things in investing, so oil prices should continue to rise.

In reality, oil remains one of the most volatile commodities. While the spot price of benchmark West Texas Intermediate crude rose 7.9 percent in 2011, it wasn’t unusual to see huge swings in prices over the space of days.

Editor's note: This story originally ran on Nov. 21 and was the second-most-read story on HAI in 2011.