Well ofc. The "take a screenshot" stuff was a bug which have been corrected and dealt with since.
But as said in one of the articles I quoted, Graphic Cards drivers never had to deal with the possibility that an "external" source might have access to the ressources of the graphical card. So their might be potentially other bugs/exploits which haven't been discovered yet. (and this doesn't apply only to WebGL anyway, but also to silverlight, even if Microsoft won't point it out)
I never meant to diss on WebGL, and ofc, Microsoft standing point is once again a commercial statement in the "Browsers battle". (even if it is, somehow, a lost battle anyway imo.)
Unlike audio, I think 3D might be an argument, though, to attract more users to a peculiar browser.
The "bad point" for Microsoft is that they can't win any monopoly over browser (seeing that FF and chrome are also available on windows OS and widely used).
The users have the choice happily, the dullness falls back again on the devs that will work to make their app compatible with all available browsers.
As a sidenote : Welcome back Ash, hope you had some nice rest.