I am fascinated by Buddhist philosophy and I even go to meditate in the temples, but I have to say I think Tolles 'Power of Now' is one of the worst books I've ever read. Much of what he says is completly unfounded and some of it he appears to have made up entirely on his own.
Ironically, the act of spending years of your life thinking about how you view the world and then putting it into a world best selling book whilst setting yourself up as a completely enlightened spiritual master, is just about one of the most egocentric things a person could do (talk about being a megalomaniac!!) - and it is completely at odds with the eastern concepts of dissolving the ego which he speaks of. As an individual I find his psychology disturbing.
Other parts of the book are taken from other concepts that are already well established, I am not critising him for this because he is disseminating some useful mindful techniques - but most of this work is discussed in the various Buddhist philosophies, especially zen and it isn't attributable to him - although to be fair to him he didn't claim that it is his.
His comment about human evolution was so completely misinformed that I don't even know where to begin to say why it was wrong. He shouldn't write about things that he doesn't understand.
Commenting on what Beetzart said.... he does suggest that science cannot study some of the things which he discusses and so it can only be explained by mysticism. This is a complete disregard of all the years of published research and academic study that has been done (that combined covers thousands of years) and he clearly has no comprehension of any of it. His opinion on this matter is based not upon knowledge, not upon wisdom, but upon a complete lack of understanding of several entire fields of research. He falls just sort of attacking science outright, and I suspect that his publishers told him to back off if he didn't wan't to find himself in a trouble.
If you really do want a good western interpretation and dissemination of Eastern philosophies such as Zen then try the works of Allan watts - but be warned it can be heavy going.
Despite all I've said, I would recommend this book to some people. Many people have found his work very useful and it has helped them in their lives. Helping people to over come pain and anxiety is a noble cause, and if people have found his book life saving then some good has come from it. If this book has helped you that is a good thing, and I would not want to put people off something if it can help them with anxiety and depression.