Discovered today that Pixie pranksters DO give a faction hit, while the tricksters in GFay, DO NOT. So if you're farming pixie dust and want to keep your unraisable faction in tact, stick to the tricksters.
So far, I've found 2 quests and one trade skill that relies on pixie dust. The before mentioned ranger and rogue quests in Kelethin, and baking. It's odd that at 30th level I have to run around killing these cute little, well, pixies just to get my baking skill to 200. Much like wisps, it seems one of the more desired commodities (dust in this case) is found on the most diminutive of creatures. Of course, they do make a nice squeak when you hit them for 75 points of damage.
There is a Pixie Dust quest out of the Ranger guild in Kelethin. Being a loyal Soldier of Tunare, I will go to any length for my fellow rangers. It builds faction, xp, gold, and gives loot. Can't see these pixies posing a menace to the safety of the forest, but I'm in no place to question my guild. They are no problem for a 6th level anything. My mino axe makes SHORT WORK of them. May Tunare guide your hands to do her work.