Has anyone found out what "buseblurshader" does in the INI file? It's set to 0 by default. Is it some cool effect that I should enable?

It is for enabling Bloom lighting -- not sure if you can use both it and HDR at the same time so usually it is off by default if you are using HDR ( bDoHighDynamicRange=1 ) so turning it on will most likely make you turn off HDR (not sure which takes precedent if both are enabled or if it just causes the game to not launch if you have both turned on !)