Does killing the spiritual leader of a terrorist group make the targets of terror safer?
In 1987, Sheik Ahmed Yassin created Hamas- calling it the Palestinian wing of the Muslim Brotherhood--the group now claiming responsibility to many of the suicide bombings and other terrorist acts against Israeli civilians. Yassin has been in Israeli prison, and released in exchange for Israeli agents held by Jordan. Often, during the peace process during the Clinton years, Yassin was under house arrest by the Palestinian authority...to, of course, little avail- he was released fairly easily.
Israel tried to assasinate him last year, with a quater-ton bomb. This failed, and Yassin stepped up the rhetoric favoring Hamas' terrorism. Yesterday, Israel sent two missiles into his lap as he left morning prayers.
I reckon the question is two-fold: 1) does the Israeli "assassination strategy" work; 2) will this particular assassination work?
The Times doesn't think so--at least in this particular circumstance, and I'll agree--particularly with this paragraph from today's editorial:

Ultimately, any argument that the assassination was "worth it" is undermined by the fact that both sides will sink deeper into their separate passions. The hard, tragic truth is that the Israeli-Palestinian conflict is locked in a cycle of violence in which assassinations, suicide bombings and mutual demonization seem destined only to grow, feeding the sense of victimhood that is consuming both the Jewish state and any future Palestinian state.

Now, that graph seems more geared to the overall strategy- and I, again, agree. My growing hunch is that terrorist organizations are not like states. (that part ought to be obvious) But I would argue that terrorist groups are much on the opposite end of a spectrum in the relationship of leader to group.
Taking out the leader of a totalitarian regime has significant effect--the third reich just loses itself without Hitler. In a representative democracy, the effect is comparitively small--the US didn't crumble with Kennedy's assasination. It seems that a terrorist group would suffer even less from the assassination of its leader; especially when the leader is spiritual more than organizational.

PS
I think Bush agrees, to some extent, that this wasn't the wisest tactic (depending on the meaning of "restraint"). From yesterday's press briefing:

Q With Israel's killing of Sheik Yassin, do you see that as -- do you agree with Israel that this was an act of self-defense? And do you support Israel's policy of targeted assassinations?

MR. McCLELLAN: Well, our policy on the last part of your question there remains the same. It is unchanged. In terms of the first part of your question, we always have said Israel has the right to defend herself. We also always have said that all parties need to keep in mind the consequences of their actions. I would point out that Hamas is a terrorist organization. Shiek Yassin was personally involved in terrorism. It is important, as we have emphasized time and time again, for the Palestinian Authority to take action to dismantle terrorist organizations. It is also important during this time period that all parties should exercise restraint and do everything possible to avoid any further actions that make it more difficult to restore calm in the region. We want all parties to get back, focused on the President's two-state vision, so that all people in the region, Palestinians and Israelis alike, can realize a better tomorrow.

(emphasis mine)