Well, Tango has an open thread on it over at The Book Blog. It's an important concept to understand as it's our, and many others, common way to boil down player value into a single number.
While there are criticisms of WAR, many of them stem from misunderstandings of the model behind the final number. So if you have any nagging doubts or are unsure of some aspect of it and want to know more, head over and ask the man himself.
If you don't feel like doing that, post your question here and somebody might be able to assist you.