Programming Collective Intelligence

Amazon rather accurately recommended Programming Collective Intelligence by Toby Segaran for me. One reviewer said:

...the author describes how the most popular of all neural networks, backpropagation, can be used to map a set of search terms to a URL... to try and find the page best matching the search terms. Instead of... proving the math behind the backprop training algorithm, he instead mentions what it does, and goes on to present python code that implements the stated goal... The upside of the approach is clear -- if you know the theory of neural networks, and are not sure how to apply it (or want to see an example of how it can be applied), then this book is great for that.

Sounds like something I'd want to play with.