Heh. Not too many people play Daemons, so it's not surprising that some aren't familiar with Fateweaver.
Fateweaver is a Lord of Change that has inferior stats to a normal Lord of Change but has a multitude of special abilities that make him one of the most deadly characters in the entire game. Most important is his special rule called the Oracle of Eternity which allows Fateweaver and all other friendly Daemonic units within 6" of him to reroll failed saves of any kind - much like the Eldar psychic power Fortune. Thus, having Fateweaver in proximity to any unit of Daemons makes them significantly more resilient.
The downside to Fateweaver is that he's extremely expensive points wise. He weighs in at over 330 points and has a poor set of characteristics for a Greater Daemon. He is also forced to take a Leadership test every time the enemy successfully causes a wound on him (no mean feat when you take Oracle of Eternity into account) - should he fail the test, he is immediately removed as a causality.
I personally use Fateweaver pretty frequently. He tends to hang out among a bunch of Lesser Daemons (most commonly Horrors of Tzeentch and Bloodletters) which makes both of these units extremely resilient and allows them to go about their business without much need to worry. Once a unit of 9 of my Plaguebearers was hit directly by a Basilisk, but because of Fateweaver's influence only a single model died - yes, that's right. Just one!