I agree that crediting should just be a common courtesy (not only to thank the person who did the work but to let other people know where to find the icons if they like them), and leaving a nice/polite note asking someone to credit is totally cool... It's just when people downright attack others for not crediting exactly how they want it - or if in some cases the coding didn't work (I know sometimes if you miss something smile when crediting icons it doesn't show up) or maybe they just missed something for some reason that I get a little bit annoyed. Asking politely is one thing, downright attacking is another.
Thanks for your opinion! It's really interesting to see where people are on this.