I was also very, very skeptical about this. But I have to say, it worked for me. I read this book in desperation after learning Dvorak, getting a fancy Kinesis keyboard, and getting expensive physical therapy (massaging of my forearms, hand strengthening exercises) to no effect. I repeat, no effect.
I don't know what else to say. It still sounds like bullshit to me, but it worked when all of the other methods did not.
When talking about physical therapy, did you ever consider referred pain patterns [1], like neck/shoulder muscle tension causing pain in the wrist/fingers?
I found the Trigger Point Therapy Workbook [2] quite enlightening in that regard. Maybe you should think about doing some weightlifting or jogging instead of trying to strengthen your hands :)
I was in a similiar situation a few years back, had to stop working due to the pain. Went to a loads of doctors, tried medication, fancy keyboards, changing chairs, improving postures, raising monitors, switching mouse arm etc. It all helped a little, but nothing solved it. 12-18 months of gym/pilates helped in the end, after gaining strength in my hands, wrists and arms I was able to go back to full time working again, without feeling pain.
I don't know what else to say. It still sounds like bullshit to me, but it worked when all of the other methods did not.