Take for instance alternative energy: it's is coming on the scene in a big way all over the world, and likely it will be a huge part of our future energy generation. However, does this mean we should jump with two feet, wallets in hand, in to clean energy company stocks?
I once read an example of a similar exploding industry over 50 years ago: the airline industry. The ability to fly anywhere in the world revolutionized how we live and travel. In only decades, airline flights have gone from luxury to a common affair. But what if you invested in the airline industry back when it started? Turns out you'd have been better off in other industries- airlines have had consistent difficulty growing their stock prices compared to other sectors.
Remember to simply diversify and spread your portfolio among several industries which will reduce too much exposure in one area. Check out my Stock Market page for more information on diversifying!