2012-06-01 : Adding loyalty counters to a planeswalker in order to activate a loyalty ability isn't an effect, so those counters are not doubled.

2012-06-01 : Any -1/-1 counters that are placed on a creature because of wither or infect are also not doubled.

2012-06-01 : Effects that place a counter on a permanent include that permanent entering the battlefield. For example, a creature that normally enters the battlefield with one or more +1/+1 counters will enter with twice that many +1/+1 counters on it. A planeswalker will enter the battlefield with twice its starting loyalty counters.

2012-06-01 : The chaos ability is cumulative. For example, if you roll {CHAOS} twice in a turn, tapping a land for mana will cause two mana abilities to trigger.