A link post (ht naked capitalism), as there is current reporting on activity at Yellow Stone by the BBC:
Yellowstone Has Bulged as Magma Pocket Swells . As one of her commenter pointed out, the Brits even made a movie about it.
I tend to view the super volcano scenario as a serious one; they have caused problems within recorded history. Of your various “end of the world as we know it” (EOTWAWKI) scenarios, they tend to be one of the more erratic ones. When they have caused historical collapses, to the extent that we are able to ascertain that they have, they appear to have been localized and of the “slow” variety.