My values with the MMA7455L seem a little strange to me. The MMA7455L is in 2g measurement mode, and the device is mounted top facing up.
Having said that my X, Y, Z are as follows:
X = 3F
Y = 3A
Z = 10
I am expecting Z to be closer to 3F as per the data sheet (http://www.freescale.com/files/sensors/doc/data_sheet/MMA7455L.pdf)
Any idea why this might occur?