Where do you get your ideas?

The single most common question people ask writers - especially SF/F writers - is "Where do you get your ideas?" The assumption always seems to be that ideas are hard to come by.

But it's not really the ideas themselves that are hard.  For instance, anyone can sit down and come up with a grocery list. The trouble is that "broccoli, milk, hamburger buns, toilet paper" is not normally perceived as story material. But as soon as you ditch that perception and start looking at the possibilities...