So when I used "learning of evaluation functions" as a segue to shift from Game trees to learning, it may not have looked
much more than a contrivance of convenience.
Turns out however that this has almost biblical importance. One of the first successful computer programs to use machine learning
(and the program that pretty much gave the name "Machine Learning" to the field) is Samuel's Checkers player. Samuel was an IBM researcher
who developed one of the first checkers playing programs, that learned to improve its performance by learning evaluation functions.
Here are few links:
http://en.wikipedia.org/wiki/Arthur_Samuel#Computer_checkers_.28draughts.29_development (definitely see this--you will be impressed at how many buzzwords you can understand now ;-)
http://www.ece.eps.hw.ac.uk/~pym1/private/docs/sutton/node109.html (slightly more technical)