Stability
I can attest to the instability of the My Book series. I bought a 1TB version just over a year ago to act as an external backup drive and to take all of my data with me when I went travelling. It is ridiculously easy to knock over and consequently, it's died after less than a year.
If anyone buys this, I strongly recommend that they find some way of wedging it upright to prevent any premature drive deaths.