I don't think it would take much for AQ to add a couple bombers in other countries. Time will tell, but I would would take any straight up bet against the Polish building being terrorist related - eg, I think it better than 50%.
Other countries better be on heightened alert now.
All commuters in the US --- Watch out!
That's the objective, terrorize people. The reality is that your chances of being the victim of a terrorist attack are probably on the same level as being struck by lightning. Probably less. People need to be alert, but they also should carry on with their normal routine.