Rulings

• 2008-05-01
  If the permanent is already untapped, you can't activate its ability. That's because you can't pay the "Untap this permanent" cost.
• 2008-05-01
  If a creature with an ability hasn't been under your control since your most recent turn began, you can't activate that ability, unless the creature has haste.
• 2008-05-01
  When you activate an ability, you untap the creature with that ability as a cost. The untap can't be responded to. (The actual ability can be responded to, of course.)
• 2008-05-01
  The exiled card is played using the normal timing rules for its card type, as well as any other applicable restrictions such as "Cast [this card] only during combat." For example, you can't play the card during an opponent's turn unless it's an instant or has flash. Similarly, if the exiled card is a land, you can't play it if you've already played a land that turn. If it's a nonland card, you'll have to pay its mana cost. The only thing that's different is you're playing it from the Exile zone.
• 2008-05-01
  If you don't play the exiled card that turn, it remains exiled but you can't play it.