This is not directly related to Kdenlive, but I was just very surprised to see my laptop doing real time video effects and compositing very smoothly on my browser, when sometimes previewing my movies in Kdenlive has hiccups. You can watch it here if you have a modern browser (I used Chromium 15):

http://badassjs.com/post/16583192105/seriously-js-a-realtime-node-based-video-compositor

Can we have such smooth real time effects on Kdenlive too? :)