I was sold a WD Mybook and the sales rep said it would work with Chrome OS. It worked for a while and then I got messages that “one or more partitions would not mount”. To my relief I found that I could access the data on a PC at the local library (even though I declined installing the software because I didn’t have the admin passwd and the staff wasn’t about to give it to me). So even though the drive is nonfunctional on the Chrome Book, it appears you can get your data through a PC. I’ll update the ituation as more info comes available. I also read that disconnecting the data cable without properly shutting down the external drive could lead to corruption of the drive but that would not explain why the data is still readable on a PC. Have to look into how to properly shut down a USB drive in Chrome OS… (what happened to plug & Play?).
The My Book drives are not officially supported yet on Chrome OS.