I'll chime in. Though a brewing newbie, I work at a cheese plant and sanitation is very important. Actually the three sanitizers we use all the time are chlorine, iodine and an acid sanitizer. Every year we have the rep from out chemical company come in for sanitation training. A few things he has said that fit with the questions/comments in this thread:
1. Sanitization is not cleaning. Forget what you hear in adverts for Scrubbing Bubbles, bubbles don't scrub. You need to remove the "gross soil" that can harbor bacteria before you sanitize. This is cleaning and often requires manual action like scrubbing with a brush or scrub pad.
2. Sanitizers are formulated to work perfectly at the recommended strength. Adding more doesn't make anything more sanitary, it just messes up the process. Unless you're trying to remove paint as one poster mentioned. You'd think that as a rep for a chemical company he would want us to use as much as possible, but that's not the case.
3. Never mix acids and chlorines. You will make mustard gas. So keep the bleach away from the star san.