NCsoft's dime. If your account was inactive as of December 1st (and you've got a retail code applied and haven't been banned), you're eligible to play Aion for free through 8:00 a.m. PST on December 13th.
NCsoft has also extended the double XP period for the entire duration of the reactivation event (as opposed to two weekend periods). Soul healing discounts of 99% will still happen on the weekend as originally announced. Finally, instance timers have been considerably reduced. For example, Kromede's Trial now features a four-hour lockout timer (in place of the usual 22). Check your timers with the /checkentry command for more details.