I'm currently using Natty. I've used adobe's version of flash found on their website, the one found in the depository, and finally the one from sevenmachines ppa. All the flash plugins have the same issue: the video on youtube and the playback controls fail to load. The audio works just fine, as does the html page itself. Just no video, or controls.
Same issue happens on Google Chrome and in Firefox. Further making this issue strange is that it's only limited to youtube and no other video website.