This often triggers me to do a mini-boardwipe (pyroclasm, infest, etc..) or standard removal as soon as I see it. I don't want to see that mana open to start really draining life. Smart players will probably use this on T3 when their draw allows, giving removal protection and allowing you to hold Disfigure (or similar) back. T4 gets even better (2 vamps for mini-wipes can be turned into bleed, and allowing 2-drop removal; of which is black's specialty.