Remember the headline from a few days ago about the impending supernova from "nearby" recurring nova T Pyxidis? T Pyxidis is a star which goes boom every 20 years, but hasn't had an event since 1967. This week some astronomers suggested T Pyxidis is headed for supernova, one of the aftereffects of which would be the stripping away of the Earth's ozone layer, massively increased gamma radiation, the creation of millions of Incredible Hulk-like monsters, and the eventual destruction of life on earth .
As it turns out, we'll probably be fine. Our friends the Gormogons point us to a more sober analysis from Discovery's fantastic Bad Astronomy Blog. T Pyxidis is 3,260 light years away. Even if it does become a Type 1a supernova--rather than a less-powerful Type II supernova (wouldn't it have been easier to have Division IA and Division IAA?)--earth is too far away to feel the effects. How far? About an order of magnitude of 10. The mistake the astronomers seem to have made is that they were using gamma-ray strength data not from a supernova, but from a GRB (gamma ray burst).
In conclusion: No supernova yet; no danger if there is a supernova; no marauding Hulks; no extinction of life on earth. There's a lesson in here somewhere.