It seems that Internet Explorer won't be getting WebGL support any time soon. In a TechNet blog post Microsoft explained that it will not be supporting WebGL, due to a number of security concerns - none of which are likely to be addressed, as they are fundamental to the working of WebGL.
The problem, as Microsoft sees it, is that WebGL gives web services too unrestricted access to graphics hardware. Moreover, Microsoft has concerts that vendor-specific vulnerabilities could surface (as different GPU manufacturers produce their own drivers, and tweak the hardware in their own way), making for a security nightmare.
As a result, "[Microsoft believes] that WebGL will likely become an ongoing source of hard-to-fix vulnerabilities. In its current form, WebGL is not a technology Microsoft can endorse from a security perspective. We recognize the need to provide solutions in this space however it is our goal that all such solutions are secure by design, secure by default, and secure in deployment."
It's not all bad news, though. Although Microsoft won't support WebGL in its own browser, plenty of others will. Firefox, Chrome, Safari and Opera all either already support the standard, or are adding support in future versions - even iOS 5 will offer some WebGL capabilities, although only to iAd developers, not via the browser proper.
Even Internet Explorer users unable, or unwilling, to change browser can still get a semi-solution, in the form of Google's Chrome Frame. But, really, if you're in an environment where IE is your only option, WebGL support is probably the least of your worries.