I, personally, went shadow right away with my priest and never looked back. I consider myself a pretty hardcore raider (and nicely geared I might add), and generall hold the #3 spot in a 10-man and #8 or 9 in a 25-man. If you want to avoid pulling aggro, here's a few tips...
#1 (most important) - download Omen Threat Meter or any other type of threat meter, so you know how close you're getting to passing up the tanks threat. If you pass it, immediately hit Fade and stop DPS until it goes back down.
#2 - If you find yourself in a raid with a tank who just can't seem to hold aggro, drop VE. Believe me, half the time it's not us; it's a poorly geared tank. You must drop VE when this is the case. The most important thing to keep up at all times is VT. Keep in mind, the more damage you do, the more mana you give to the healers (who are main healers in the first place). By the time you get to 25-man raids, the tank should be nicely geared and capable to manintaining aggro. This is where I go all out and add VE.
#3 - If you're a "raiding" Spriest, you MUST have 3/3 Shadow Affinity. It reduces your threat by 25%. I once forgot to respec for a raid after arena, and didn't have Affinity on. Needless to say, I was a lower on the damage meter than I'd like to have been.
#4 - get the Subtlety enchant on your cloak. It only drops your threat by 2%, but hey...every little bit helps.
Side note: They're nerfing our VT in the new xp. Short version: Blizzard decided to take 60% of our mana regen and give us a useless AoE. Lower level Spriests will notice this more than the high-level "geared" Spriests will. In addtion, we're supposed to scale better when it comes to DPS, so those geared Spriests shouldn't be as affected. Increased damage = increased effectiveness of VT.
#1 (most important) - download Omen Threat Meter or any other type of threat meter, so you know how close you're getting to passing up the tanks threat. If you pass it, immediately hit Fade and stop DPS until it goes back down.
#2 - If you find yourself in a raid with a tank who just can't seem to hold aggro, drop VE. Believe me, half the time it's not us; it's a poorly geared tank. You must drop VE when this is the case. The most important thing to keep up at all times is VT. Keep in mind, the more damage you do, the more mana you give to the healers (who are main healers in the first place). By the time you get to 25-man raids, the tank should be nicely geared and capable to manintaining aggro. This is where I go all out and add VE.
#3 - If you're a "raiding" Spriest, you MUST have 3/3 Shadow Affinity. It reduces your threat by 25%. I once forgot to respec for a raid after arena, and didn't have Affinity on. Needless to say, I was a lower on the damage meter than I'd like to have been.
#4 - get the Subtlety enchant on your cloak. It only drops your threat by 2%, but hey...every little bit helps.
Side note: They're nerfing our VT in the new xp. Short version: Blizzard decided to take 60% of our mana regen and give us a useless AoE. Lower level Spriests will notice this more than the high-level "geared" Spriests will. In addtion, we're supposed to scale better when it comes to DPS, so those geared Spriests shouldn't be as affected. Increased damage = increased effectiveness of VT.