From Diablo Wiki
Leaderboards are a feature coming to Diablo 3 in Patch 2.1. They are basically the UI display of the ladders, which Blizzard is calling Seasons in Diablo 3. Leaderboards will display the top characters in each Season, ranked by various criteria.
The updated rankings will show the highest Greater Rifts cleared (and the time required) by solo classes and groups of 2-4 players. These can be filtered to show everyone on the server, your clan, just your friend's list, or even other players in your location such as at a LAN party or Baang. Leaderboards will also record the first 1000 accounts on each server to reach level 70 (with each class) as well as the first to complete the various seasonal Conquests, which are special seasonal Achievements.
Greater Rift Leaderboards
Greater Rift leaderboards will be split between both Hardcore and Normal gameplay modes as well as Seasonal and Non-Seasonal characters. To help encourage a variety of play styles and allow you to measure yourself against similar competitors, we’ve also broken up Greater Rift leaderboards into the following categories:
- Solo play for each class (e.g. top players for Barbarian, Demon Hunter, Crusader, etc.)
- 2-Player Groups
- 3-Player Groups
- 4-Player Groups
Some Leaderboards will be Season-only. For example, Conquests are only tracked on Seasonal characters, so these Leaderboards won’t have a non-Season equivalent. The same will be true for Seasonal achievement points. In addition, because Conquests and achievements are account-wide, their associated Leaderboards will not be split between Normal and Hardcore (even though some tasks may require playing a particular mode).
The full system has not yet been demoed, but once the Patch 2.1 PTR starts players will get a look at it.