I know, I know, who the heck has or uses a Blackberry Playbook?
1. Audio always resets to maximum volume when starting any video. Volume control is normal after that, not affected by pause, resume, jumping around video timeline, etc.
2. The preview image that is present before you hit play doesn't display any more. (This only applies to the page for the video itself and not the thumbnails when choosing a video.)
3. Not 100 percent of the time, but, when starting a video it can take long enough that the Playbook throws up a warning that the video may not be streaming fast enough to be watchable. I just tell it to wait 2 or 3 times and it will eventually start. Generally the video plays perfectly fine once started and you can jump around in the video to various points without inducing the warning message again.
I suppose the good news is that the actual playing of videos is still fine!
(I've tried resetting cookies, clearing cache and all that usual jazz. This is with the latest version of the OS and built in browser.)