Myers-Briggs types

I've been spending some time again looking at my Myers-Briggs personality type. For anyone who's never looked into this, try this online test. I'm an ENFJ - about 5% of the population. We're nice, but I reckon we must have a bit of a martyr thing going on - always trying to help other people. I'd really like to get a book about it and maybe do a more comprehensive test - 72 questions doesn't seem enough. For a personality quiz, though, it's pretty spot-on, but I'd just like to know more. Last time I took it I think my results were a bit more extreme. I must be mellowing with age. Or having an off day. Being moderate sounds awfully dull.