Almost every great idea I've had, I've gotten while taking a shower. It used to be in that moment where you add conditioner to your hair, and the bottle instructs you to "wait about a minute." Almost every great idea popped into my head during that minute. Eric Meyer told me the other day that he's had the same experience, and calls the shower "the thinking box." The remainder of my great ideas come to me when I'm alone, and driving a car for more than an hour (there also has to be no traffic).
As the world becomes more information-laden, I wonder if the moments I can think absolutely clearly and free of distraction will be fewer and farther between. If I was born 50 years ago, would I be producing twice as many ideas? Maybe this is why everything for the past ten years seems retro or derivative of earlier ideas. We're loading our lives with so much minutia that our creative thinking suffers.
(An hour after I posted this, a thought came to me regarding that last point I made. All the great artists I can think of in the last century were terrible with money. They were highly creative, but didn't worry about pointless stuff like taxes or prices or savings. Conversely, the artists that made a lot of money were pretty crappy artists or did things wildly popular yet not that creative.)