Suicide bombing in Afghanistan is in decline, and Strategy Page tells us why. The quick summary is that Afghans are extremely resentful of the tactic, the Taliban lack the technical resources to support suicide bombers, and the coalition forces have been successful in dismantling the few cells which carried out these gruesome acts of terror.
They conclude their piece with this observation:
Suicide bombing is described as a weapon of the weak. What it cannot be described as is a weapon of the victorious. In the last few decades, whoever used suicide bombers not only failed to gain anything, but saw their cause harmed in the process. You can draw your own conclusions, as have most Afghans.