Writing a basic I2C or SPI driver for your sensor is only 1/2 the work (often less!).  All of the real magic is doing something with that sensor data, and that often means getting your hands dirty with some basic DSP (digital signal processing).  I stumbled across this paper on filtering sensor data to balance a device, but it shows a lot of the tradeoffs and decisions that go into making real-world use of raw sensor data.  (See The Balance Filter: A Simple Solution for Integrating Accelerometer and Gyroscope Measurements for a Balancing Platform by Scott Colton.)  DSP is an extremely interesting field, and there a lot of fun challenges to be had, but picking the right filters (with the right performance characteristics) can take some thought.  Have any fun stories yourself where a favorite filter saved the day?  Post the up in the comments below!