Multiple instances of shroud on the same permanent or player are redundant.
September 30, 2011 · Innistrad
The controller of an attacking creature with trample first assigns damage to the creature(s) blocking it. Once all those blocking creatures are assigned lethal damage, any remaining damage is assigned as its controller chooses among those blocking creatures and the player or planeswalker the creature is attacking. When checking for assigned lethal damage, take into account damage already marked on the creature and damage from other creatures that's being assigned during the same combat damage step, but not any abilities or effects that might change the amount of damage that's actually dealt. The attacking creature's controller need not assign lethal damage to all those blocking creatures but in that case can't assign any damage to the player or planeswalker it's attacking.
June 17, 2011 · Commander 2011
The controller of an attacking creature with trample first assigns damage to the creature(s)
April 1, 2011 · Duel Decks: Knights vs. Dragons
Attacking doesn't cause creatures with vigilance to tap. (See rule 508, "Declare Attackers Step.")
February 4, 2011 · Mirrodin Besieged
Attacking doesn’t cause creatures with vigilance to tap. (See rule 508, “Declare Attackers Step.”)
October 1, 2010 · Scars of Mirrodin
Attacking doesn’t cause creatures with vigilance to tap. (See rule 508, “Declare Attackers
February 1, 2010 · Worldwake
Attacking doesn't cause creatures with vigilance to tap. (See rule 508, "Declare Attackers Step.")