I have to side with the Will Save crowd on this one. The rules should build on simple principles to create a consistent system for simulating events and determining outcomes. That's really the beauty of the D20 mechanic. Avoiding an effect from taking damage sounds like a saving throw to me. The throw also covers all classes consistently and simply. A Will save sounds logical, and favors spellcasters. Rangers and Paladins will be slightly disadvantaged but aren't supposed to be primary spellcasters. They can improve their odds by taking feats (maybe a feat that allows them to take a fortitude save?) or by higher wisdom scores. Save DC = 10 + Base Attack Bonus. Doesn't create alot of new rules. Stays consistent. Perfect. That'll be my house rule from now till Computers replace dice altogether.