I feel that way about games too. Sometimes I need something visual as opposed the the text I'm usually immersed in. And I suspect that those games use different parts of the brain, so in essence, you rest the parts you've been using while working out other parts and of course, they're not totally disconnected.
I do the same thing, but with Freecell or Sliding Tiles. Easy enough to do automatically without thinking and quick enough to leave to rush back to the story when a great idea sneaks in.
When I was in grad school, I would play Tetris when I needed a break from writing - and I used to dream about it, too! I remember I had a dream one night in which I played the perfect game over and over. I was actually exhausted when I woke up - and confused for a few moments, b/c it felt like I had never gone to bed. I actually had to check my computer to see if I really had been up playing it all night. 
I do this too. My favorites are Tetris and Collapse.
Now I downloaded Snug and -- this is not going to be good.
I have definitely dreamed about playing Tetris, too. Have never thought about it as a productivity measure, though!
Commenting by HaloScan
