Your sensor returns acceleration, and this is not directly translatable into degrees.
You could use the output of your sensor to create a turn rate gyro, then integrate that output to get a heading but that is a complicated project.
But if you are looking for an easy way to get a heading signal into the arduino, have a look at using a heading hold gyro like this: http://www.bphobbies.com/view.asp?id=A3828158&pid=A3678070
It provides an output pulse width proportional to heading. I don't know how linear it is, but it works well as a kind of autopilot on the rudder of my radio controlled helicopter.
A simpler method of getting heading is use an electronic compass, SparkFun has one that should be easy to integrate into the arduino.
Are you trying to solve a specific problem, or just having fun?