You should try just reading the values and sending them to serial.write directly and take a look in the serialmonitor to see what kind of numbers/data you get in.
Trying to use pre-built sketches (particularly complex sensor based things with multiple libraries) it can be difficult to troubleshoot.
I've had similar problems with the i2c sensor in my setup though the ones coming in over analog pins worked fine almost immediately (http://arduino.cc/forum/index.php/topic,117638.0.html).
I'm currently still having a problem with the i2c (magnetometer) as the data I'm receiving on the computer isn't right, so I think something is going funny between the Arduino reading the sensor data over i2c (as two bytes) then combining it into one byte, then me splitting it into two bytes again to send out.