2008-05-01 : If a creature with an {Q} 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 : If the permanent is already untapped, you can’t activate its {Q} ability. That’s because you can’t pay the “Untap this permanent” cost.

2008-05-01 : If you don’t play the exiled card that turn, it remains exiled but you can’t play it.

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 : When you activate an {Q} 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.)