Or, should I ask, when will it happen?
An excellent article argues for exactly why Israel will destroy the Iranian enrichment facility at Natanz. Most importantly, it reasons that Iran can't particularly retaliate against Israel (at least in a meaningful sense), since if Israel wanted, it could simply bomb six major oil refineries and cripple the entire Iranian economy. Of course, it doesn't consider what Iran's big friends Russia and China might do to involve themselves in the kerfuffle, which could be an issue.
I'm actually surprised Israel hasn't bombed yet. We knew they wanted to at the end of the Bush administration, since reportedly, Bush wouldn't give them the technological support that they wanted. Now you have Benjamin Netanyahu in charge, there is little chance of Israel taking anything sitting down.
Maybe, though, the author is dead wrong. There might be a lot more going on behind the scenes than we know. Nations act in unexpected ways, so I guess we'll just have to see.