your question would be better answered in the salvia divinorum subforum just a little bit down from this exotic plants one. www.erowid.org has great info. I'd say a few grams.
I got mine from bouncing bear, tried just one dried leaf now(half hour later) no effect and it taste pretty damn bad, guess i just need to up it more
This is going to sound horrible, but you really need as many as you can possibly hold in your mouth. Make sure you clean your mouth with listerine and rehydrate the leaves or it won't work either.
i've heard people using 16 leaves for a nice trip....make sure you don't swollow as stomach acid deystroys the active chemicals.
I couldn't imagine a Salvia trip lasting more then 10 minutes. It's so intense. I would love to try a quid though. I have before and it was so disgusting I couldn't even hold it in my mouth.