GL_ARB_Debug_Output - what do you need ?

If you could talk with Graphic Drivers Developers about GL_ARB_Debug_Output extension, what type of messages you would ask them to be printed out by driver? What use cases should this extensions consider? What debug messages would be most important for you?

Please write concrete use cases, all suggestions will be taken into notice!

More info about extension itself:
http://www.opengl.org/registry/specs/ARB/debug_output.txt

Thanks,
Karol