The My Book is Western Digitals largest line of external hard drives and arguably the largest overall.
I bought a 500GB My Book because I telecommute and needed the portability. I also needed it simply because I was running out of free space on my internal hard drive but didn't want to install a new one. The simple solution was an external.
The portability on the My Book is great. It's sturdy, compact and light. It's small and light enough to fit in my briefcase and sturdy enough to have survived multiple drops onto the floor.
The My Book's 16MB data buffer is great for streaming things like documents, text files, and music to the computer, but for things like HD video you will want to transfer them over to your primary harddrive which, at 7200RPM, is a pretty speedy and painles process.
If you need a new external hard drive, look no further than the Western Digital My Book.