Does anyone have a source for the numbers they are stating? I had assumed, and I admit this is an assumption, that Magic Resistance merely protected your Magicka. Alchemic damage (Ravage Magicka, Lingering Damage Magicka), weapon enchantments of Diminishing, Sapping, Depleting, etc, and spells such as Thunderbolt (does 60 points of Shock damage to Health and half that to Magicka) are mitigated by Magic Resistance. Health damage is not mitigated at all by Magic Resistance by my understanding.
Magic is spells cast by you and others.
Magicka is the resource you cast with.
Magic spells cast by others can lower your health. eg Fireball.
Magic resistance reduces the health damage you take from magic spells cast by others.
Here's a source. http://www.uesp.net/wiki/Skyrim:Resist_Magic