For weeks, the Pakistani military has been cutting off escape routes out of South Waziristan and softening targets with air-strikes. U.S. drone strikes and intelligence-capabilities have also lent a hand, taking out top commanders to create a growing list that most recently includes the leader of the feared Uzbek militants. Partly due to the coming winter and partly due to government and tribal urgings, civilians have been leaving the area.
Many officials, both on and off the record, have essentially said that the attack is coming very soon. Here's what is worth noting;
Pakistani Major General Athar Abbas says he has approximately 28,000 soldiers to take on an estimated 10,000 militants. It's not clear whether Abbas' figure includes paramilitary troops such as the Frontier Corps, or whether his estimates of militant strength includes militants that plan to stay out of the coming fight. Much of the Pakistani delay on this assault, which some felt should have come months ago, has been due to government attempts at not just building local "lashkars", or government-supported militias, but also because of attempts to peel away as much support for the Pakistani Taliban and their foreign-militant allies as possible. The extent of their success in that endeavor has yet to be measured.
Perhaps most important is the coming winter. Snows are expected by late November, giving the Pakistani army no more than about a month and a half before the mountainous terrain becomes ever-more treacherous. While the Pakistani army has a lot of experience fighting in such environments(see; the 80's), the home-field advantage of the militants could be much greater with such conditions. Unless, of course, part of the strategy is to push the militants into one heck of a freeze. It would not be surprising if the Pakistani military tried to use the winter to weaken and demoralize the militants in conjunction with continued and intensified air strikes.
Imtiaz Gul, who knows this region about as well as anyone could, calls South Waziristan an intelligence "black hole". So have generals involved in the military planning. On the record, Pakistani Army Chief General Kayani described the area with the same adjective, adding; described Waziristan as an intelligence black hole. "We have to move in,". Once they have moved in, and once the winter has set in, it is unclear whether they will press on with a ground offensive or position themselves for another offensive once the snows melt.
Why the Pakistani military is letting everyone know is debatable. They could be trying to convince as many civilians as possible to leave in addition to forcing the fence-sitters to decide between the militants, Switzerland-esque neutrality, or siding with the government against the Taliban and foreign fighters. What isn't debatable is that there will be blood, and this represents the best chance to capture Osama bin Laden since 2001.