Effects like BlueBanana are fine, but even simple transitions like dissolve cause the framerate to go anywhere from 35-60 all the way down to a slideshow. Not sure why this is, but I'm using the latest build (as of Feb 27th on Arch). My media is mostly h264 FLVs (with one MP4, though this does not seem to make a difference) and I am using the x11 video output. Oddly I have noticed that for single video tracks towards the top of the composting stack x11-OpenGL is the fastest, but for anything else x11 with the direct x11 render option is fastest for normal playback. Neither of these are enough to stand against transitioning however. Funnily enough, everything I've tried from h264 inside an FLV, MP4, and MOV to a ProRes MOV file seem to play back all the same, but when transitioning they all seem to slow down horribly. I'm not sure if this has been fixed in the latest development version, I suppose I'll see tomorrow.