There was a thread about this in the Budget Travel forum not too long ago. I'm too lazy to look for it though.

Sleeping in Airports can be awesome! I found a spot in Heathrow one night that was a children's play area. It was about 10 feet long with about 7.5 feet of it protected by a 4 foot demiwall. I nuzled into the cove and slept on this cushion that was as thick as my backpack. I slept like an infant until the cleaning staff discovered me the next morning.

Was I stuck for a layover? Nope, I'd just run out of money travelling, and couldn't afford a hostel for the night. Many other people sleep in airports too, it ain't all that bad!

http://www.sleepinginairports.com