Since the thread was bumped…
I can’t help thinking that this topic is a little out of Mythbuster’s scope. While interesting & fun science, it’s there’s no myth to be busted on this.
-B
There’s always been pseudo-scientific speculation into applying the structural properties of spider silk to the creation of materials with high tensile strength, but I think it’s mostly reserved for comic strips (Spiderman) and sci-fi fantasy tech. I think I recall something called “carbon-fiber arachno-weave” which was used to make strong but incredibly light armor in some fictional SF universe … an anime freak friend of mine told me about it. Honest. 
Regarding the dilatant body armor/Mythbusters discussion, I know there was there an episode dedicated to the history and future of body armor on one of the edutainment networks recently … A&E, History Channel, Discovery … ? I don’t know if it was Modern Marvels, or Battle Gear, or Mail Call … each network has their own little weapons technology shows and they all sort of blend together in my mind, but they discussed the topic of dilatant kevlar materials which were lightweight and flexible, but which could absorb and/or deflect high-speed projectiles. Quite similar to what was shown in that Google Video that Squink posted a few days ago …
Spiderwebs are one of the strongest and toughest fibers known, so it wouldn’t surprise me if someone had considered making some sort of armor out of them. However, they’re very difficult to synthesize or cultivate in sufficient quantities, and I think in the past few years they’ve developed synthetic nanofiber composites which are even stronger and tougher.
But they’re pretty stretchy, which isn’t normally something you’d want in body armor. Who cares if it stops a bullet after it travels 12 inches beyond the point of impact?
I saw a guy on TV recently who had invented a beenie for skiers and snowboarders that had a layer of silly putty type material in it. The idea being that when their head hits something hard and unforgiving the beenie will take the impact. But it doesn’t look like you’re wearing a helmet, so you don’t lose the cool factor of skiing.