Why Iran will not do it
(1) There is no way that Ahmadinejad or any other Muslim would drop a bomb on Israel. We all know that if a Muslim drops a bomb on Jerusalem he will be destroying the dome of rock, which would guarantee him a thousand years in hell.
(2) The explosion will kill more Muslims than Jews
(3) The Explosion will be followed by Israeli nuclear attack.
Why Israel will not do it
(1) Israel cannot pull off this kind of operation without the help of the US; they are going to need cruise missiles, satellite information, refueling, and the coverage to get out. To avoid a significant Iranian reprisal, The US has to bomb Iran like the first one hundred days of the Desert storm, destroying not just the nuclear installations, but all military capabilities and the infrastructure. No American president would sign off on such a plan and no American generals will give that option to any US president, just like they did not give it to Bush.
(2) At this time, almost every country in the world which buys oil from the Middle Eastern countries has one or more warships floating on the gulf. There is also Two American battle groups, and 1500 Iranian speed boats, some of which are equipped with the fastest under water anti-missile missiles in the world (200+miles an hour), there are an unknown number of Israeli submarines, as well as three Iranian submarines with medium and long range missiles, such an armada can turn the US & Israeli attack into a international nightmare.
(3) Since the Iranian air defense system around the installations are manned by the Russians, an Israeli attack will kill Russian soldiers. Americans avoided killing Russians even at the height of the cold war. Considering the fact that there will be dead Russian soldiers, we can assume that the world would get very close to an international conflict.
(4) In the first few hours of the attack, regardless of Israel's success or failure, there would be a war which would include Iran, Israel and the US.
(5) In the second phase, there will be Saudi Arabia, Kuwait and any of those warships of different countries.
(6) The third phase will bring the Hezbollah, Syria and Lebanon into the picture. In other words, regardless of the real facts about Iranian nuclear program, and success or failure of Israel, the new war will be more dangerous an will involve with, almost all powers of the world.
(7) I am sure you recall the attack on Iraqi nuclear plant in early 1980s. Although they had practiced it for a long time, the only person who was informed about it was Ronald Reagan, and that was only a few hours before the attack. The fact that we are talking about such possibility is the best evidence of their intention not to attack Iran.
Let's examine the different possible outcomes based on the information which is available to us.
(1) If Israel & US attack are successfulAt the best Israel would cause severe harm to the installations in Natanz (centrifuges), Bushehr (Russian built reactor), Tabriz (long range missiles), Arak (heavy water). The installations in Parchin and Chaloos will not be dented.
(2) If Israel & US attack is not successfulA Russian early detection system might inform Iran of an impending attack, and although there would be some harm to Iran, it would not be as successful as expected.
(3) Unknown Results: The war might pan out in a different fashion, simply because of our limited information.