The whole concept is extremely fascinating and very compelling - perhaps accounting for its popularity amongst new age thinkers. However, morphic resonance is not supported in the scientific community and the hundredth monkey effect is largely considered to be an urban myth.
I have always been interested in treehouses - at one time several years ago, my interest became so acute I decided to search for existing books on the subject and surprisingly, a new text had just been published. Subsequently there has been a proliferation of other books and articles - a number have appeared in the New York Times.
I was both surprised and excited to see this display of tree houses in Madison Square Park, juxtaposed against the New York cityscape - see another group shot here. This is a public art project called Tree Huts by Japanese artist Tadashi Kawamata. If you don't mind a bit of artspeak, you can read about it here at the Madison Square Park website or here at the Tree Huts blog.
Although I realize that all the recent interest in tree houses is almost certainly due to cross pollination, I just love the idea that it could be morphic resonance :)
Note about the photo: The gold topped building in the background is the New York Life building - you can read my posting and see its spectacular night time illumination here.