I think any western military action, and possibly even any Israeli military action would be a grave mistake at this juncture. The current regime is becoming more unstable, though perhaps not on a daily basis.
For the Theocracy to truly be defeated, they need to be brought down internally. Persians are notorious for their unbelievably venemous resentment of any 'foreign meddling' and any blatant foreign aggression - even something as small as an Osirak-type strike - will strengthen the regime and the military to the massive detriment of any homegrown reformers.
Twice before, Iran has come close to throwing out the mullahs, once in the mid-eighties and again in the early 90's. The first time, the Iraq war boosted the Ayatollah, the second time it was Western saber-rattling (specifically, the 'Axis of Evil' speech... I'm not even kidding on that, it was a big driver of votes for Ahmadinejad.
The single best weapon anyone has against the mullahs is the Iranian people themselves. The problem is that the west must resist the temptation to intervene.
Highly relevant:
Persian Nuclear scientist killed in mysterious bomb blast. Now I don't know that this was the work of 'foreign agents' or if the guy's wife (or even the regime) just didn't like him and the government's just taking advantage of the situation, but even stuff this small causes a big furor.
EDIT:
More details in today's Globe.Also very relevant: Saw an article elsewhere that claimed the projections for Iran having a bomb have been pushed back to five years or more, though I can't seem to find it.
this editorial seems to have seen the same report (and seems to parrot my view), but doesn't mention the source for the new figures. If correct, it means the west has at least some time to wait.