This is an important thing to think about. OpenGL is the standard and only option under non-Windows platforms, but now lets consider the idea of OpenGL being the main graphics API under Windows.
I know MS may be pushing their own API, as someone may say, but this does not make alot of sense. Direct3D is free, they dont make money out of it. And using OpenGL does not affect their commercial products. Thus we are safe on the market side. 
What we need is a WHQL qualified drivers.
Khronos don’t make OSes and have no say whether a specific driver is authenticated to be installed on a Win/Mac/Linux OS.
Promotion of GL can be done only by exposing many many customers to modern software that uses it. Or have an one-man-army constantly check all possible paths and nag driver-vendors for bugs. It’s quite possible to make a demo-app, that verifies most paths.
A nice looking demo that users can download and run themselves to check on their OpenGL drivers might be nice. However, the demo app should be written using standard OpenGL. So no hacks for certain drivers or whatsoever. It is in the end a test for checking the standards.
If such a demo is maintained properly and it looks appealing, it might have a chance of becoming popular under end users. Sort of compare it with the acid3-test that tests the css standards compliance of webbrowsers.
If it gains enough popularity and it is supported by Khronos, perhaps AMD and nVidia will get interested in market their products with `100% performance on OpenGL-xyz test’.
Well… one can only dream. But perhaps for OpenGL such a way might be the most feasible way.
[edit]Such a demo should not only run under Windows but also on other platforms that use OpenGL. If a simple benchmark is included as well such a demo could replace glxgears in Linux.
(dreams a bit further ;))[/edit]
I agree, a conformance test, made by the ARB.
However, when an application using OpenGL fails, the end user will blame it on OpenGL, if there’s an alternative API option that works perfect. With no alternative, it will be the application fault, since other applications using the same hardware and an alternative API works just fine. If there was no alternative, then users will blame it on the OS/platform since similar applications work awesome on one platform with an alternative API.
In conclusion, it’s not the hardware, it’s always the software.
IHVs are safe.
And I noticed someone keeps taking my rating starts 
Very funny that happens whenever I suggest something that may help the poor API. However, you can ban me guys from these forums, I’m a Direct3D fan, happily!!!