I tried some times for use Kdenlive on video editing. I tried to edit a simple videoclips based on DV PAL Widescreen. Sources are coded on DV avi format. I only apply some effects and create some keyframes for volume and opacity but kdenlive crash each a few seconds or minutes when I use preview screen. I use last version Kdenlive 0.7.8 with last MELT 0.7 on Ubuntu 10.10 64 bits.
I think this program is not usable at all.