Creating a Plugin System

On techbase we have a tutorial about extending your application with a plugin system. However, it's unfinished and some people need it as you can see on the talk page. So if you feel like passing your knowledge on, please fill in the missing sections to complete this tutorial. Just make sure to keep it as simple as possible, of course you can also change what's already there. Btw, we once had such a tutorial for KDE3, maybe you can copy some text from there. It would be awesome to have it for KDE4 as well :)