Here is some technical information about chain. Think in terms of initial "elongation", not "stretch".
http://www.diamondchain.com/support/.../wear_life.php
and from their FAQs: 12. Roller Chain Stretch (Elongation)
Why is my chain "stretching", elongating, too quickly?
ANSWER: Proper lubrication is critical in achieving the maximum wear life of any roller chain. As the chain articulates around the sprockets, the pin and bushing wear. This wearing causes the elongation, or "stretch", in the chain. Lubrication of these surfaces through proper lube application or the utilization of Diamond Duralube or Ringleader O-ring chains can greatly increase the wear life of the chain.
I've found that a decent quality chain has less initial elongation than the no-name-brand stuff sold for cheap go-karts.