There are some details that in software usability (the big word of all and nothing) are important: icons are for sure one of these.
A good icon should immediately tell you what is meant to be and how works the functionality behind it.
I will show an example how an icon is badly representing the functionality that “hides”.
A KDE’s Plasmoid can be resized and the resizing icon is like that:
Resizing icon
Without knowing anything about software everyone could guess that clicking to that icon and moving to direction bottom-right the plasmoid will be bigger (both width and height).
Before resizing
So I tried to use it and surprise! Holding the left click on the icon and moving to bottom-right direction the plasmoid’s width becomes bigger, but the height is smaller!
So the icon is not representing the functionality or the functionality is not correctly implemented, either way I don’t understand how I can resize a plasmoid without ending up in such a mess!
During resizing, moving mouse to bottom-right
After playing around a bit I discovered that there is an identical resizing icon on the left side (you need to move near to left’s border) that moving to the same direction makes the window smaller (both width and height); so we have two identical icons, but with different behaviors and both are not what the icon is representing! This is a big usability issue.
I will post more things like that in my blog in future, as you know (or maybe not), details are important for me and for my work 
Note:
issue reproduced on Kubuntu Linux 8.10 that ships KDE 4.1.2 as default WM.
