The Deadman's Revenge
But large-scale attacks take long preparations, a few months at the very least - it is also a function of the magnitude of the operation.
So, even if Bin Laden's comrades in arms started plotting revenge right yesterday, we won't see them in action for large-scale operations before the end of the year. And with the almost obsessive attention to terrorism of this age, I doubt that another attack of 9-11 scale can be mounted, at least in the West.
Terror plans already underway may be hastened to conclusion, but they would have to be at an advanced stage already. So I don't see much of an effect on attack plans already underway.
What can happen is action by isolated fanatics acting out individual jihad. It happened already in the past, and can happen again in the future. However, while these attacks can cause death and spread fear, their real potential is very limited: isolated individuals cannot perform actions that require... more than one individual; their supply routes for weapons and explosives are restricted and time constraints make difficult to draft complex and articulate plans.
We might see some attacks that result in the death of the attacker and maybe a few people unfortunate enough to be in close proximity, but not much more. At least I hope.
Revenge attacks are not a sufficient reason to adopt more extraordinary anti-terror measures. Also considering that a good part of the measures of today are more for the show than for effect, actually.