I hate the noodles. I have quit other people's bands, and fired people from my bands over noodling situations that could not (or would not) be rectified.
That said, I am with Tim. I will hit a couple of chords, maybe a quick lick when I walk onto the stage, just to make sure everything is proper with the rig. Nothing like going for the first big downbeat and hearing something REALLY wrong, or worse yet, nothing at all. Both will eventually happen to you if you play for long enough.
Finalizing settings during the first tune is usually not an option for me, as I am too busy handling the vocals. I can't really look very professional stepping off the mic in the first verse to fix my amp settings. In an emergency, I've had to do it, but I try to avoid it at all costs. If something is fishy that I didn't catch, I just have to live with it until the first song is over, then make quick adjustments.