Israeli counter-terrorism officials explain that a major reason for the continued drop in Palestinian terrorist attacks inside Israel (only two last year, while killed eleven people), has been the destruction of the terrorist organizations that plan and carry out these attacks. In the past year, Israeli counter terror operations in the West Bank resulted in the arrest of 187 Palestinians who were involved in terrorist activities, with another 130 killed. One Islamic Jahad group, which operated in the northern West Bank, was basically destroyed last year, with the loss of 33 of 38 members (killed or arrested.) This group had been responsible for several successful attacks in Israel. During 2006, two Israeli soldiers and six civilians were killed in the West Bank, which is the result of good intelligence, and the careful planning of operations. The Israelis have a large informer network in the West Bank, and several hundred police commandos selected for their ability to pass as Palestinians (the commandos speak Arabic, and are from families who once lived in Arab countries, but were forced to flee by Islamic radicals.)
The damage done to West Bank terrorist groups has been so extensive that most of the remaining cells spend a disproportionate amount of their time avoiding the attention of the Israeli police. Because of this, more terrorists from Gaza are showing up, as well as aid from Hizbollah in Lebanon. The Gaza terrorists can leave via Egypt, and enter the West Bank via Jordan. Hizbollah operatives also use the Jordan route. Border security with Jordan is tight, but not perfect. Attempts to smuggle weapons and cash are often foiled, but a lot of this stuff does get through.
However, the basic Israeli tactic, of detecting, and going after, the terrorist cells that recruit, train, equip and guide (into Israel) the suicide bombers, has proved highly effective. It takes quite a bit of organization and skill to get a suicide bomber into Israel, and if you keep the terrorist groups in disarray, and constantly watching their backs, fewer bombs go off inside Israel.