It's just a small thing, but had annoyed me for a while. The "Screen Locker", from Iguana > Configure Desktop > Display and Monitor > Screen Locker, has a slide show option. Gnome seemed to have dumped this, so I was happy to see it in kde.
I'm not big on fancy transitions, anyway, and the random ones here were impossibly slow. Why transition every five seconds to a new picture if it takes 30 seconds to paint a new screen? https://bugs.kde.org/show_bug.cgi?id=182104 is the reported bug, and the fix still works. Edit ~/kde4/share/config/kslideshow.kssrc, and add "EffectsEnabled=false" after the last line.