I enjoyed this:

Saturday Morning Breakfast Cereal via Cosmic Variance

The laws of physics are very fine-tuned. Change them even a a little bit and it would not be possible for us, or indeed any life, to exist. The valence electrons of Hydrogen are a particularly obvious case. Two electrons would fill the electron shell, making it impossible to form compounds (i.e. water, hydrocarbons). It would be Helium.