The use of in-camera stabilization is not as effective as in-lens stabilization, particularly with longer focal length lenses. This is why Canon and Nikon chose to go with IS in their lenses and not their bodies.
In-lens stabilization is better than in-camera stabilization, but IS (Canon) or VR (Nikon) lenses are very expensive for someone looking at a starter DSLR. I can only speak from my experience...I can take blur-free pictures with a shutter speed of 1/10 sec. when not using a tripod. Since the K100 has the same in-camera mechanism as my K10, I would expect comparable results. That isn't bad for a starter DSLR with a kit lens that costs only a little more than the cheapest IS or VR lens.