Erik Jantzen of iTulip believes that alternative energy will be the next asset bubble. In his view, the coming mania will dwarf the internet and housing speculative run-ups. After the past few months, you can see the plausibility to this kind of view.
Our own view is that alternative energy will transform our world, and the best way to ease this transition is through informed, long-term, socially responsible investing. There will be much volatility along the way, of course, but it would be a shame if speculation crowds out the patient money.