At the moment, the best way to learn about Product Management is simply to go on one of the courses offered by the likes of Pragmatic Marketing, Silicon Valley Product Group or 280 Group. I went on the Pragmatic Marketing course a few years and am really glad I did. Highly-recommended. If you want to do a course in the UK your options are more limited, Co-herence is the only one I know.
If you don’t have the time (and money) to go on a course then your thrown onto reading. So far my standard recommendations are: Crossing the Chasm and The Inmates are Running the Asylum. Neither of these is about product management but they do cover some of the necessary ground. (And if you are a Product Manager they are essential reading.)
Well, the people at Pragmatic seem to have a book on the way. In the meantime they have made available an e-book called The Secrets of Market-Driven Leaders. I have not had time to read it in full yet but what I have read I like. For anyone trying to work out how to manage a product (or what Product Managers are) it might be the best thing yet.