If a character in Dark Heresy has the talents to wield two weapons and chooses to wield two automatic one-handed weapons, what happens when they declare a full-auto attack action? Will there be two attacks or only one?
There will be two attacks. On page 190 of the main rulebook, under the Full Auto Burst heading, it says that if you have two pistols in your hands you may fire them both. Page 197 discusses two-weapon fighting, and while it doesn't explicitly say that you make two attacks, note that two-weapon fighting with a melee weapon and a pistol does call for resolving each attack separately. Also, there's no stated bonus for using two weapons other than the potential for two attacks, which strongly indicates that you get to make two attacks -- otherwise, you'd never do it.
As a sidenote, also per page 197, you may only lay down one area of suppressive fire even with two full automatic weapons.