my friend ate 2 and didn't get high enough but felt it a bit. Takes me 2 to be pretty high, takes only 1 for my other friend. Depends on tolerance I think.
People are different.

Microwaving works because you're making the weed hot enough to prepare the absorbing into the peanut butter. It's just good to be sure. As long as you don't microwave it too long (takes about half a minute to start burning) 15 seconds is decent for preparing and finishing the crackers.