Pakistan and Afghanistan have serious, and worsening, Taliban problems. And I'll admit openly that I believe that negotiation with the Taliban is necessary for peace--they are a huge chunk of both countries and they are well left-out of the political process. I'm not entirely sure how I feel about the recent deal in Swat to grant Sharia law in two Pakistani districts for peace. The US has openly given it a hard time, but apparently privately supported it.
So far, it's off to a rocky start. The top Pakistani official in Swat has been kidnapped by the Taliban, though may have been released. This represents a serious problem with the deal that plagues many deals with non-state actors: the "group" is loosely-affiliated enough that not everybody will agree to what one negotiator says. So, even though this cleric that dealt with Pakistan is probably genuinely in favor of not continuing to fight, his promises aren't particularly credible because he does not have authoritative control over the region. So other Taliban members will largely shrug their shoulders and continue doing whatever it is they do.
The other serious problem with such an agreement is that it can create a safe haven. Even if the Swat valley dies down in violence, Taliban from other regions, including Afghanistan, may well use it for sanctuary as they gather munitions/plan attacks/spread propaganda/communicate/whatever it is they do. The Taliban is a big, diverse group of people with many diverse interests. One of those, obviously, is punting NATO. No amount of Sharia law will actually get the fighting in Afghanistan to stop, and insomuch as there is more solidarity between Pakistani Taliban and Afghani Taliban than there is between Pakistani Taliban and the West (hint: there's lots more), those Pakistani Taliban will continue to assist their Muslim brethren in attempting to boot the Western Imperialists. Such a deal might actually make the lives of the US harder.
So, how is this a mixed bag? Well, it might show that negotiating works. When you lack the capacity to win at costs acceptable to you, then you negotiate. This is something we failed to understand in Vietnam--and, frankly, as much as Western liberal media liked to link Vietnam and Iraq, Afghanistan holds the analogy much better. We're dealing with a large insurgency by a huge portion of the country that genuinely opposes 1) the guy we've put in charge (in this case, Karzai), and 2) our presence. In Iraq, most of the serious problems were between Iraqi ethnic groups. Now, it does happen that the pro-Karzai factions are largely northern ethnic groups and the Taliban are largely Pashtuni, so the analogy is not perfect, but it's closer. Currently, Afghani Taliban are unwilling to negotiate as long as NATO sticks around. But if they see their lives made easier by successful peace deals, they may reconsider.
Like Iraq, making concessions for a lull in violence is likely to allow the government to retrench itself. Pro-government forces in Talibani areas will likely be more free to promote the government's agenda, and Afghani army/police will be able to at least step into Talibani areas to improve the government presence and administration in these areas. The many tens of billions poured into the country for economic development and education will be more effective. Hearts and Minds takes over, and it can work, especially with a mastermind like General Petraeus managing the operation.
Of course, there are lots of complaints about deterrence and appeasement. But one cannot actually beat every problem into submission. From the point of view of the Taliban, the US showed up to boot them out, and one cannot "deter" them into idly sitting around and letting the West run the show when they genuinely think the West is out to get them/Muslims/Afghanistan. What negotiation (in parallel with serious security operations, obviously) will show is that the US is willing to deal reasonably with the concerns of this large chunk of the country.