While the real-estate bubble in the US burst a few years ago, in many countries around the world it never did. In countries like Canada, China and Australia, price levels along a number of metrics (compared to incomes, rent levels etc.) have now surpassed those of the US at its peak! The Economist has a great interactive tool that allows you to get a handle on just how bubblicious some housing markets are.
You can use the tool here, which allows you to compare the state of housing across several countries. For example, one can see that the price-to-rent ratio in the US is about at the same level as it was in 1980, whereas for New Zealand, price-to-rent ratios are about 4x what they were in 1980!
These bubbles have been inflating for some time, but for the first time in a while there are some signs some of these housing markets may be turning. For example, there are reports of falling prices in certain areas of China, which would become big news if it spread. Several sites are dedicated to tracking such issues; for example, this site provides daily details about the impending doom of real estate prices in certain Canadian markets.
Whenever these bubbles do burst, one potential implication could be a global reduction in demand for commodity products. There seems to be a prevalent sentiment among investors that commodity prices can only rise over time; but if history is a guide, this is far from a sure thing.
China consumes more of several commodities (including energy, copper etc.) than does the US, despite an economy that is less than half as large. Such a situation may not be sustainable, and if demand for such products were to drop as bubbles are burst, a number of assumptions about the prices of certain commodities could be worthless.
Be careful with your assumptions; remember to always consider downside risks with respect to your investments.