As a type I diabetic, I use both my forearm and my finger tip for testing. While I find both to be almost painless (admittedly I may have built up a tolerance) arm does hurt slightly less, and more importantly, does not callus like the finger tip. However, in times of rapid blood sugar fluctuation, arms are delayed by about 10-20 minutes, where as fingers are not.

Interesting, I assumed the delay would be more like a few seconds or half a minute at most.

Still, why not do it on the side of the finger? It has to be as updated as the tip, but it has a lot less nerve endings.

Sides hurt (me) more. Don't ask why, no idea. I know some doctors suggest the sides, for that exact reason however.