As discussed in this blog post (includes a video of controlling Second Life from a HMC6434) the USB-to-serial firmware that ships stock on the Arduino R3's ATMega16U2 can be replaced with a USB HID joystick firmware, allowing you to use sensors such as an accelerometer as a 'joystick' for any program that takes USB joystick input.
The MMA8452 example uses the MMA8453_n0m1 library for the accelerometer & the newer LCD library for an I2C LCD. The Comp6DOF_n0m1 library may also come in handy.
The idea & the joystick firmware (as well as the original Arduino firmware) came from this blog post.