I installed Lubuntu and noticed there were no video file thumbnails in the file manager, pcmanfm. I did some poking around and it looked like some people were saying because of some changes in Gnome 3, pcmanfm wasn't able to create video thumbnails anymore.
So, I installed nautalis, using it with the --no-desktop option, but it also wouldn't give me any video thumbnails.
I have strange problem with thumbnails in my Ubuntu machine.
I was using Ubuntu with Cinnamon 1.8 from stable ppa and it was good but then Cinnamon 2.0 came out with some broken packages uploaded to stable ppa nad things gone wrong...
Anyway after few updates Cinnamon started to work normaly except Nemo - there are no thumbnails at all, only icons.