While I've never used these properties I would imagine the property list automatically get cleaned up when the associated window closes. Just to be on the safe side though I would be inclined to remove properties as part of the windows close code at the very least.
You could always take a look at the Steam Hardware Survey. They don't directly check OpenGL support (not sure why not) but you can at least get an idea of what cards are being used by gamers more by checking the video card results. That might give you a bit of insight anyways.
Find content
Male
