I don't really understand why a mage/warlock/priest that has an end goal of raiding wouldn't take Tailoring.
I mean, you can obviously play however you want, but the level 70 gear you can make for yourself is unreal. Nothing like sitting around a boss loot session and watching everyone going crazy rolling for T4 gear while you sit back and laugh to yourself when you realize your gear is already better than T4.
If money is a major concern for you (for me it's not - I'm content with my basic flying mount), then sure pick up a gathering skill to go with it. Just pair it with Tailoring - so worth it.
As for enchanting - it is a huge money soak, I'll certainly concede that. However, I enjoy being able to enchant my own gear, plus the ring enchants are caster only. Not a huge draw, but that's still +24 spell dam I wouldn't have otherwise. I still make money selling arcane dust/greater planars/large prismatics. Not as much as another gathering profession, but I get by.
There are arguments for Herb/Alc, but we have guild pot makers for that, and there's no way I'd pass on Tailoring.
/steps off pedestal
Edited, Aug 3rd 2007 9:58am by Azzwurms