Since the upgrade to Kubuntu 13.10 today I lost the borders around maximized windows. How can I re-enable them? I tried this and of course changed
false, but it doesn't work.
The ability to show borders on maximized windows was removed from kwin in KDE 4.11. You can find more information about this decision in bug 299245. Basically, the implementation was a hack that caused multiple bugs, and the developer said that the proper place for this feature was in the decoration rather than in kwin.
So, this feature was added to the oxygen window decoration. Unfortunately, this change has not made it into a stable KDE release yet. Once released, the option will be available by going to System Settings->Workspace Appearance. Then, if you're using the oxygen decoration, you'll be able to click on the 'Configure Decoration' button, go to the 'Fine Tuning' tab, and check 'Display window borders for maximized windows'.