at the moment.
I dont think the physical whereabouts of troops has any bearing on future attacks. If they are going to happen they will happen regardless.
That said, the longer the presence in Iraq, right or wrong, the more intense those attacks are likely to be.

Remember that most of the people (so far traced) that organised 9/11 and London 7/7 were not residing in Afghanistan or Iraq, they were already in the UK, USA, or in Germany or Holland.

The fact there hasnt been a terrorist attack in the US since 9/11 is therefore unrelated, in my opinion, to the placement of troops overseas.