Recovering irrationalist: I feel the same way. The most interesting book I've read about this is George Ainslie's "Breakdown of Will". Ainslie uses the experimentally verified theory of hyperbolic discounting to build a model of why we do things like make promises to ourselves that we then fail to keep, and othe rforms of behaviour related to "akrasia".

http://books.google.co.uk/books?id=7dTHzcaTRpIC&dq=%22breakdown+of+will%22&pg=PP1&ots=PSAPRlxfkD&sig=4jmS627eK3oMDHtcSVHrZ3IsNoA&hl=en&prev=http://www.google.co.uk/search?q=%22breakdown+of+will&ie=utf-8&oe=utf-8&rls=org.mozilla:en-GB:official&client=firefox-a&sa=X&oi=print&ct=title&cad=one-book-with-thumbnail