Here is a VERY, VERY large video that I came across.
It's a good example of how a nylon tow strap can maim/kill. It's about 1/4 of the way through. Replay it couple times and notice the damage it did to the pickup's rear tail gate and cab rear window/dash/windshield. Luckily, no one was in the way.
*WARNING* Big video - No dial up
http://www.offroadkrayzie.com/videos/TheBigStuck.mpeg
Nylon tow straps are great. Getting a running start at pulling someone out (like the guy in the black Dodge did) is a good way to get somebody unstuck from a bad spot. The strap will stretch, then the rebound plus the recovery vehicle's momentum makes for alot more pulling force than just the recovery vehicle alone could generate.
Make sure you keep your straps new and clean. Sand (the stuff that glass is made from) can really eat a tow strap. A strap in good, clean condition won't snap like the one in the video.