I know that this is the iPad forum, but I'll throw this in anyway since the iPhone4 and iPad1 use essential the same CPU/GPU: My iPhone 4 running 4.3 is playing m.youtube.com just fine in HQ and SD. This leads me to conclude that the issue is either on Apples side with the iPad build, or only effects a subset of videos. Can you post a specific video that is showing this problem? Also, those of you having issues, are you using iPad1 or iPad2? It could be a driver issue with the new GPU.