Siri is able to tap into Wolfram Alpha, which is a computational knowledge engine. Because of this, there is an entire bank of knowledge that can be drawn upon by simply asking Siri. One helpful piece of information that can be computed by Wolfram Alpha is nutritional information for food. For example, you can ask things like, “What is the nutritional value of an Egg McMuffin?” Siri will look up the information and present it all in a nutritional value label right on your iPhone, iPad (Mini), or iPod Touch screen.
You can also ask Siri to calculate specific quantities or servings of food. For example, “What is the nutritional value of one cup of black beans?” Siri will respond with the nutrition information for the serving size you specified.
For more things you can ask Siri to compute using Wolfram Alpha, check out this article over at Tuaw.com: 10 cool things you can do with Wolfram Alpha and Siri
In addition, TeachMeiOS.com has partnered with author Erica Sadun who wrote an entire book on how to use Siri. She is offering TeachMeiOS.com users a 30% discount off her book. Get more info here: Learn How to Use Siri Book