This can 'o worms gets opened up every so often in these health threads, so I thought we'd just dedicate a thread to it.
Myself, I have lazily gotten most of my information from a single documentary:
Exhibit 1, a nice lecture on the subject by the guy who did that doc:
Personally, I tried a lower carb / higher fat diet, and it's nice. I generally felt better, and was losing weight. A couple months ago I went off it, and have been gaining weight steadily, and feeling worse
I especially get angry when I see parents trying to deny their children any fat, like only drinking skim milk etc. At a time when their brain, mostly fat, is still developing, the last thing it needs is to be is denied the resources it needs to grow.