Same problem for me:
-impossible to dowload on Youtube, dailymotion, msnvideo, myspace video, crackle, vimeo, bigthink, aol.com and wwi.tv
-metacafé, comedy central, maker.tv, and redtube do not show the "download / popup" bar
-Wat.tv (tf1.fr), aol video, ishare.redif, ted.com, youporn work
-Blinkx do no load/show the player...
Hope that wil be helpfull for MX5!!