When do you get your story ideas?

I thought this would be a liitle different twist on the question of where do story ideas come from.

Mine usually just pop into my head. IT HAPPENS IN THREES story idea came to me after a long weekend of reading. I was sitting at home in one of my favorite chairs waiting for the phone to ring for a job offer and the plot started to draw itself in my mind. :-)

Most the time my story ideas occur to me when I'm driving. You're mind is totally clear, okay not totally, because that would be scary if I was behind the wheel with an empty mind. Anyway, just the other morning I was driving to breakfast (great little place not far from me), and it hit me.

Luckily, I always carry paper and pen or my laptop with me. That morning I had my laptop so as soon as I sat down, I booted it up and drafted the first page. Now it's put away until I finish my current work-in-progress.

When do your story ideas hit? And do they compel you to write them down right away? Or do you let the plot and characters gel and when you get it all worked out you write?