Pruning to KApplication class
KDE hacker "Icefox" reports that he's been doing a lot of pruning on the Qt4 version of KDE's KApplication class:
Lots of exciting stuff is going on for KDE4. Recently I have been hacking on KApplication mostly. Over the years KApplication turned into a storage location for anything that couldn't find a home. A month or so ago I printed out KApplication and QApplication api docs for some weekend reading and planning. Taking it in small, mannagable blocks I have removed quite a lot from KApplication and even more can be done once Qt 4.1 is released. But what makes this really exciting is that as each patch got in, the interdependency in kdelibs was reduced. This will help us in the goal of separating the kde libraries. Yesterday, after a little work I was able to run a KDE application (trusty KTron) using QApplication. Work still has to be done, but we are on our way.
Doing some very unscientific tests you will be happy to hear that your average KDE application seems to drop 3MB in memory size just by porting to Qt4.