I have an Lenovo T420 (Sandy Bridge HD 3000) Notebook.
If i get the news on Phoronix correctly my notebook should show Opengl 3.3 or at least Opengl 3.2 Profile.
But i only get one Opengl 3.1 Profile and below that an Opengl 3.0 Profile Output.
Im just using your ppa, no others. Where is the error (or is that as desired?)
ii xserver-xorg-core 2:1.14.3-3ubuntu2+gd~s amd64 Xorg X server - core server
PS. If you need specifically youtube hd, you are much better off with 3rd party youtube watchers (found in xbmc, umplayer etc) which support proper hardware accelerated playback.
Also, in my experience the Firefox plugin works much better than the Google one (which doesnt seem to like any kind of hardware acceleration with radeon/mesa, be it 3d or 2d with mesa resulting in no webgl and tearing fullscreen playback).