-or maybe I just need to get out more, I dunno....but hey, did you know that fine sandpaper will remove rust stains from the toilet bowl? OK stop laughing, we have very hard water in the well, and no matter how much I clean, the rust stains are a pain to get rid of. I've used stromg cleaners, vinegar, pumice-and today I took some fine grade sandpaper to the bowl and know what? Like new. That's what.
Keep in mind you need the fine grade paper, and you can't scrub the hell out of it or you'll ruin the finish on the bowl, but otherwise, this is a nice chemical free way to deal with rust stains. For regular old hard water build-up, I like white vinegar. If you soak a rag in it and leave it on the tap overnight, it will be sparking by morning. That works great on chrome, but the toilet bowl was really bothering me (look, I don't ridicule the stuff that keeps you up at night).
Sandpaper-go get some and marvel at the results in your own loo.