The US has done an about face and endorsed a key suggestion of the Baker-Hamilton report that it talk to Iran regarding the instabilities in Iraq. According to The Economist the US will join in regional talks (Iran and Syria included) in Bhagdad on the security situation in Iraq. The US has abandoned its insistence that Iran constrain its nuclear developments as a precondition for talks.
The Economist is vague on the reasons for the US change of heart but suspects it might reflect a gradually improving security situation in Bhagdad as the 'surge' in US troop numbers impacts. The pressures imposed on Iran via a threatening US military posture and increased troop commitments in Afghanistan (which increase pressures on the 'other side' of Iran) put the US in a position of greater power and plausibly make it more interested in bargaining.
Whatever the reasons there is little to lose in talking.