I must say again, Scrum-deleeicious idea! And this coordinates so well with all the stash busting knit alongs I've joined for the summer.
If you're a bit unsure about this (as I was when I first heard about it a few months ago) try this tactic - just get some of the yarn left overs and the "I'm not so sure about this anymore" novelty stuff out of your stash, grab a few different needles (or crochet hooks - is that allowed Hilde??? Mixed media, etc?) and just knit while watching a movie, don't even pay attention to what your doing really. Bind off and pick up some stiches anywhere on your "swatch" and start with another yarn. That's what I intend to do.
There is a good article on this free-form technique in the Summer 2006 issue of Knit.1 (page 25). The article lists a good reference for a website too where designer Prudence Mapstone shows photos of a scrumble "evolving"
That site is right here