From Blind Fighting. It doesn't state where it comes from, so I haven't the slightest idea.
[/quote]Actually, I guess it doesn't matter where it is from. From the Blindsense/Blindsight entry in the SRD:
must have line of effect to a creature or object to discern that creature or object).
I don't think Tremorsense would work either, actually.
As long as the other creatures are taking physical actions
Incorporeal creatures don't have physical bodies, and so by definition don't take physical actions.
Spectres, wraiths, and a few other creatures lack physical bodiescannot manipulate objects or exert physical force on objects.