Well, my 500 gig My Book Premium just crapped out on me. That's when I discovered that my online daily back wasn't working properly, even though it happily reported it was.
First, I tried switching from USB to Firewire, and it worked! But not for long, and I couldn't get the last 3 weeks worth of files off.
Next, I tore the My Book to pieces (literally) to get at the hard drive inside, and installed it in a standard $30 enclosure. Once I hooked that up, I was able to get a bunch more files off before the I/O errors started up again. Eventually, I was reduced to turning it on, copy a single file, turning it off, turning it on and waiting for several minutes, copying another single file... I got all but 9 files back.
Someone tried to tell me that a unit like a My Book (or other dedicated external drive) would be faster than sticking a standard drive inside a standard enclosure. Not sure why that would be so, but I won't be buying any more "disposable" external drives like the My Book.