A couple things. First, it's theoretically possible that this might not be an Islamist attack, but a military one. The gunshot to the neck is an odd addition, certainly; Islamic extremists usually count on the explosion to do its work, and don't carry out this sort of "hit". If it comes out that Musharraf IS behind this, of course, all bets are off. Pakistan will erupt.
It's kind of doing so right now, though. Riots are taking place as we speak, and show no sign of stopping. A police crackdown might be inevitable, but if it's too violent, it will itself exacerbate things.
And then there's the creepy parallel people are making: 9/11 started off with an assassination of an anti-Taliban leader in the region too. No reason to become paranoid unless you work for the CIA or NSA... but if you do, I wouldn't expect too rockin' of a New Years.