Look at a ratio of oil ($OIX, or your favorite) to USG and you'll see that it's coming in from the far right tail now, mostly from the collapse of oil price.
USG is at it's long term lows now.
My opinion is that USG is a reasonable buy right now, on that basis, for a long term hold.
Caveat emptor, I have the first of a multi-part position in place, at $14.
I don't usually get a chance to talk my book, cause I can't type that fast!!
Be well,
rr