As far as the Craft thing it depends on what d20 game you are playing. D&D doesn't specify I don't believe, at least I can't find it right now one way or another. Star Wars states that it's a no can do, at least on Wizards' site. In d20 Modern it's situational. You can't unless it's Craft (writing), again according to the Wizards' site.
Anyway you can't take 20 if there is a penalty for failure. If you fail a Craft check by 5 or more you ruin half the materials used.
So basically if you're so good you can't fail by five or more even by rolling a one then you can take 20. Otherwise you are stuck taking 10.
But, to get back on track. I knew someone who's group completely misunderstood the Cure line of spells. For example they thought that Cure Light Wounds healed (1d8+1 points)/ caster level. Not 1d8, +1 additional point per caster level.
How they missed the (up to +5) I don't know.