EverQuest, the twelve-year old MMO launched two new servers today, both of which are time-locked progression servers.  Essentially, the content is locked to specific expansions until players reach certain goals (such as downing bosses), and the majority of players vote to move on to the next expansion.  Both servers launch with the rules and content that were in the game at its launch in March of 1999, albeit with some changes (some zones have altered geometry; the leveling curve and death mechanics are both from the modern game; the map is present).  That means fewer races, fewer classes, fewer zones, fewer items, a lower level cap, and a harder game.
 
The voting mechanism was added  because previous progression servers saw the top guilds blowing through the old content, forcing progression before the majority of players may have been ready for it.  Requiring votes from players above a certain level was seen as giving the playerbase as a whole a voice.
 
There is a FAQ from SOE on the rules of the two servers.  There's also a good explanation of the differences between the new servers and launch EQ from a blog called Ark's Ark.