Mullah Omar wants to convey a feeling that this one is different than WWII for instance.........that our soil will not be immune from attack.
Should we be worried? We should always be worried about Islam, which throughout its 1400 years of existence has shown itself to be little more than organized brigandage, extortion and terror (apologies to the gentle Sufis, hated by Islamics). But I really don't think there's a plan in place or the power to carry one out.
That said, I think there probably will be more attacks, but probably lone-wolf operations. Although after I read today that the White House is celebrating the opening of Ramadan, I wasn't even sure terrorism was necessary. Just hand them the keys to the city, why don't we. Mny other states have done so over the last 1,400 years.