During a live-stream video chat today with the game's developers, D.C. Universe Online's free-to-play debut was set for Nov. 1, which is Tuesday of next week. Originally expected sometime in October, the new freemium model gives everyone two character slots and all game content as a base offering, with expansion packs and extra characters as paid extras.
Those who have spent $5 or more on the game (i.e. those who bought it at retail or paid for a subscription but choose to go free, or in-game store customers) get a premium membership, affording more character slots and a larger inventory.
Those who continue paying the game's $14.99 monthly sub (or have purchased a lifetime subscription are granted Legendary status, which gives them an big ass inventory, more than 15 character slots, and free access to expansions and DLC as they roll out.
More info can be found here.