Good advice, especially if you do a lot of bending, too. I do it the B.B. King way a lot of the time, too, though, and I feel there's more natural 'rhythm' that way--
Hold the note with just the forefinger, and let the rest of your fingers fan out-- don't force it and make yourself uncomfortable, but they should be fairly extended for this technique to work. Then, instead of thinking about wiggling the string itself around I just shake my hand. I never concentrate on how much I'm moving the string, because if you're putting that much 'thought' into it, you're bound to get uneven vibrato. The extended fingers give your hand some 'leverage' to throw around for a nice, natural (usually fast, though) vibrato.
For that really slow wavery stuff, you're usually better off with weezerboy's type of grip, though I'll still do slow one-finger vibrato sometimes.
Greg.