PhotoFlow, which I introduced less than 48 hours ago, can also be realized as a plasmoid. It is the top left applet in the screenshot above. I have never written a plasma applet in my life before, so it took me quite a while to figure out how the mechanism works. And frankly, I am still not sure whether such a kind of widget can be really useful at all.
I guess I will wait until KDE 4.1 before I place this stuff in KDE's playground. By that time, Plasma itself should already stabilize. Probably it is even better to integrate it with the Picture of the Day data engine. Or even with the slideshow plasmoid. Or perhaps do you have any other idea?