Matt Toner is the creator of this very cool site and app, that allows you to easily calculate the odds of an action in 40K.
Knowing the rough odds of a certain action in 40K is a really powerful tool. Most of the bet players can either run the numbers in their heads, or memorize odds to allow them to make smart decisions about what they should or should not do while playing. For those less mathematically inclined, this tool allows you to run the numbers on your phone or at home with ease!
Matt and I played at the SiS4 last weekend, and he is an excellent general with a really cool Necron army. Give the tool a look!