Recently I started to have some problems viewing flash videos, specially youtube videos. Sometimes they worked, sometimes they didn’t. Sometimes just the buttons in the video/flash movie didn’t work. Looks like the problem is related to some update in karmic.
The solution for this problem is to install flash-player alpha 10 (amd64) from Adobe.
There is a nice post at ubuntuforums with the steps you need to do in order to solve this issue.