If you want to tweak something in a KDE application that's not in the settings dialog, look in ~/.kde/share/config/APPNAMErc and ~/.kde/share/apps/APPNAME/.
Mount USB drives async, it makes it way faster.
Don't use cat on binaries, it will screw up the console. But you can use strings to find strings in binaries.
Read the Gentoo Handbook, even if you never install Gentoo. It'll teach you how to do things manually in the event of automated programs failing.
OptiPNG with -o 7 is slightly better than PNGCrush with -brute.
You can find some more tips in an old tips thread.