No one in the US and Europe takes the Iranian threat as seriously as in Israel. Meaning no one is coming to help Israel in case of a preemptive strike. If Iran retaliates, Israel will stand alone and completely isolated to face the threat. So far all Ahmadinejad has done is talking, so I don't think it'd be reasonnable to launch an attack purely on words. No one would come to the rescue of Israel in case it's needed.
Israeli ambassador to U.K.: Elements of left 'in denial' about 'disease' of anti-Semitism (Haaretz)
from the article: Israel should heed Obama's warning not to strike Iran