Theresa asked via twitter:
"Food science question: What is the purpose of adding baking soda to the water when boiling soft pretzels?"
Baking soda is an alkaline ingredient. Typically in a baked good, it's mixed in with the flour and combined with an acid. Under those conditions, the baking soda neutralizes the acid and creates carbon dioxide bubbles, causing the baked good to rise.
Because the baking soda in question is on the outside of the pretzels and because there's no acid to react with, we are clearly not trying to increase the lift of the pretzels. This means we want to increase the alkalinity on the outside of the pretzel.
In many ways, pretzels are like bagels. They have interesting shapes that are optimized for even cooking. They are both boiled before baking. There are differences, though. The pretzel is cooked in alkaline water (or otherwise treated with baking soda to make it alkaline on the outside). Also, the pretzel is much darker than a bagel. These facts are not coincidental.
Browning at low temperatures, such as the kind a pretzel or bagel are exposed to during baking, happens because of Maillard reactions. These reactions happen in the presence of water and certain amino acids. They are also aided by an alkaline environment.
Ann Voss asked "I thought it was a taste/texture thing?" It does, though indirectly. By allowing the browning to to happen more easily, you don't have to bake the pretzel nearly as long to achieve the brown exterior. So if you baked the pretzel long enough to get the brown color on the outside without the alkaline environment, you would impact the texture significantly.