Bayes Theorem and Naive Bayes

I've heard Naives Bayes described as "nearly good enough" for many uses. Can anyone quantify how much worse it is for various applications?

If I understood this correctly Naive Bayes uses "reasoning on the average". I'm assuming this is good for fast rough estimates at best.

Good post in terms of content; really wish he had a nice syntax-highlighted code box instead of screenshots of code

The last two screen shots are the same