2 teaspoons - rounded side down - put the tip of each spoon under the edge of the knob, gently push the handles down, knob comes off smoothly and no damage to anything underneath. Slower and more controlled than the shoelace or t-shirt method, I have seen the shaft pull right out of a (cheap) pot that way.
Last edited by MattK on Wed Feb 09, 2011 10:19 pm, edited 1 time in total.
Anything like that where you're levering against the body, you should put some fabric on top of the guitar first. A t-shirt or thin towel or whatever. Something so that you don't risk putting a ding in the finish either by applying too much pressure or slipping.