I made a post on this on another forum (around 12 hours after the assassination). I put it here for I suspect that some may find it of interest.
There are two possible groups (that I see at least) that engaged in the assassination of Bhutto.
The first one is a vanguard type force (think Zarqawi’s Al Quada in Iraq in the first year after the invasion of Iraq). If it was a vanguard type group, then the intent wouldn’t be to get rid of a western style leader (though it would be a plus) but to show that the state is impotent. This would cause other attacks by those who are also unhappy with the Pakistani government and increase the speed that primary loyalties are formed (for it seems the state fails at providing security), thus weakening the state even further. A possible secondary goal would be to weaken the social fabric of the state by creating a rift between those supporting the government and those who supported Bhutto. Though if this works too well (I.E. a full fledged civil war) it is liable to backfire on the attackers for a full scale civil war would be nearly a total war, something that the attackers would not be able to fight, though a low level burn would be something that an insurgency of that type can effectively fight in (read up on the Askariya Mosque bombings and their results as a modern example). With both, the objective isn’t to destroy the state, but to weaken it greatly.
A second possible group would be those who are opposed to her political beliefs or are against her pro western attitudes. The intent would likely be to prevent the westernization of Pakistan. If this is the case, I would assume that it would likely not be done by Musharraf. This is mainly because of exactly what is happening now, instability and people thinking that he may have been behind the attack. He already has enough people looking to kill/overthrow him, I doubt that he needs any more. I know very little of the Pakistani government and security services, but from what I have heard, I would not be shocked if it was done by a group inside the government or military, but acting independently of Musharraf. The main goal of this would be to keep the Pakistani government strong, but avoid certain influences on the government.