Several weeks ago I heard on (I think) Diane Rehm a discussion on should Israel attack Iran and if the US should help. While I don't remember all the details and can't find the exact show basically said the following;
If the US lead the attack it would at best set back the Iran nuclear effort by only 2 years.
If Israel attacked only it would at best set back the Iran nuclear effort by 6-18 months.
Any attack on Iran may cause an outright war between Iran and Israel with other countries in the area joining in most likely supporting Iran.
This one scared me. Israel's only real hope of doing lasting harm to Israel would be to do the unthinkable and going nuclear.