Darkfall Unholy Wars' equivalent to EVE Online's PLEX, a way to extend your subscription to the game while allowing you to trade for in-game currency. And if that's what's kept you away from the game, your inability to pay for your subscription by earning more currency in the game? You're in luck, as the game is offering a special one-day reactivation on September 11th for lapsed subscribers to log in, purchase D.U.E.L., and possibly get back into the game.
Players have expressed some consternation over this decision, arguing that a single day in the middle of the week is an odd time to reinstall, log back in, and try to purchase an item. Official statements by Aventurine staff have clarified that this is only a single flash promotion, and it does not rule out the possibility of other similar promotions in the future.
[Thanks to Dengar for the tip!]