Being a non-schooled, part-time graphic designer, who's learnt everything on his own during about 10 years of doing print-design, this book has provided quite a useful resource. I just bought it, and it certainly isn't completely perfect (small gripes, such as too small print and at times a bit messy layout that perhaps aimed at something artistic but fell short), but for its price, it has already done some wonders and has given me quite a lot of food for thought.
Actually, inspired by this, I designed a nice propositional layout and managed to get a good contract doing the design for a 250-page text book with loads of pictures, graphs, tables, and all those nice, giddy little bits that one can spend a ton of time with. For me, this book has been quite educational and reasonably inspirational, though if you've been through a formal education in design, this might not be up to scratch. But for every self-taught designer, I would heartily recommend this nice little piece.
I suppose the main gist of what I would say is that if you're thinking of whether or not you should buy this, my advice would be to go ahead.