2009/9/16 Andrew Garrett agarrett@wikimedia.org:
The problems you suggest are, in my opinion, examples of poor usage of icons, rather than problems inherent in icon use.
Absolutely agree. I'm personally responsible for some of the most egregious icons in MediaWiki (namely some of the default toolbar icons), which as we've found in our usability study, were utterly confusing to users and didn't help them find key functions. There are well-established visual metaphors for many concepts in MediaWiki, and then there are things which are a lot harder to illustrate, where we may do better without visuals.
Some good discussion about good/bad icons here: http://usability.wikimedia.org/wiki/Opinion_Icons
Some relevant discussion from another context: http://library.gnome.org/devel/hig-book/stable/icons.html.en
I think the Apple HIG have a lot of icon-related guidelines as well, but can't download the 27MB PDF right now to check :-) http://developer.apple.com/mac/library/documentation/UserExperience/Conceptu...