I have to agree about the book, no way do I believe Walt would allow such a highly incriminating piece of evidence to just be sitting around the house. Not through lazyness, forgetfulness, carelessness, or simply thinking there's no chance anyone will ever see it and make the connection, it doesn't ring true for me at all.
It does bother me that Hank has found out in such a cheap way, it's definately not what I'd expect from a show that has set such high standards. But this is Breaking Bad, a show that has been astonishing for such large portions of its time, I don't really want to moan too much when I feel they could do better, since the vast majority of the time they do, and easily too.