Imagine spider silk replacing fiberglass threads for example, or carbon-fiber threads. Its not fiberglass or carbon-fibler per-se that makes the material strong, its the composite. The mixture of plastic (which provides compressive strength) with fiber (which provides tensile strength).
There are a ton of composite fibers in the marketplace. I'm not a materials engineer, so I don't know exactly what people are looking for in their fibers (aside from high tensile strength). Probably low-weight, high strength... and probably low-compressive strength (or at least, people ignore the figure).
"Elasticity" in spider-silk sounds interesting, but I'm not sure if thats good or bad for a composite.
-----------
The composite for structures is going to be Reinforced concrete: Steel Rebar provides tensile strength, while Concrete provides compressive strength.
Where spider-silk (or fiberglass / carbon fiber composites) shine, are low-weight applications. Bicycles, bullet-proof armor, and flywheels. The question is if spider-silk is actually any better than carbon fiber (or Kevlar)
That's the thing: we have a LOT of manufactured fibers. Maybe spider-silk has a niche that can be used. But its competing against Carbon Fiber, Fiberglass, and Kevlar.
-----------
It seems like Spider-silk has less tensile strength than Carbon Fiber / Kevlar. However, due to its flexibility, spider-silk can absorb significantly more energy before breaking (aka "Toughness").
So spider-silk might be superior for stopping bullets in a composite weave, but it would be awful as a load-bearing structure (unless that load-bearing structure were expected to be "catching" objects a lot). Hmmm... maybe a Tennis Racket would be the ideal use of Spider Silk...