Your life total can't change. (You can't gain or lose life. You can't pay any amount of life except 0.)
1/1/2011 The ability doesn't prevent damage. Rather, it changes the results of that damage. For example, if a creature with lifelink deals damage to you, you won't lose any life, but its controller will still gain that much life. Similarly, if a creature you control with lifelink deals damage to another player, that player will lose life but you won't gain any life. Notably, if a creature with infect deals damage to you, you'll get that many poison counters.
1/1/2011 Abilities that trigger whenever damage is dealt to you will still trigger because that damage is still dealt, even though your life total doesn't change as a result.
1/1/2011 Spells and abilities that would normally cause you to gain or lose life still resolve, but the life-gain or life-loss part simply has no effect.
1/1/2011 You can't pay a cost that includes the payment of any amount of life other than 0 life.
1/1/2011 If a cost would include causing you to gain life (like the alternative cost of an opponent's Invigorate does), that cost can't be paid.
1/1/2011 Effects that would replace having you gain life with some other effect won't be able to be applied because it's impossible for you to gain life. The same is true for events that would replace having you lose life with some other effect.
1/1/2011 Effects that replace an event with having you gain life (like Words of Worship's effect does) or having you lose life will end up replacing the event with nothing.
1/1/2011 If an effect says to set your life total to a certain number that's different than your current life total, that part of the effect won't do anything.
1/1/2011 If an effect would cause you to exchange life totals with another player, the exchange won't happen. Neither player's life total changes.
1/1/2011 The ability won't preclude you from losing the game. It just precludes your life total from changing.