I'm running ubuntu on a chromebook, and am having trouble with pepper flash. I can run chromium-browser with
sudo chromium-browser --user-data-dir=/tmp/ --ppapi=/opt/google/chrome/pepper/libpepflashplayer.so
and flash video works perfectly. However, as a normal user, it loads the plugin (by checking the chromium://plugins page), but doesn't play flash video. I checked to see if normal users had permissions to read the plugin directory, and they seem fine (644 permissions)
Quicktime and HTML5 videos work without too much trouble.