The Overwatch Top 500 system is now back online! The system existed back when Competitive Mode first came out, however, it was wrongly showing people they were in the top 500. Now it seems Blizzard has fixed the system and made it live once more.

There have also been some changes to the way the system works. Once someone breaks into the Top 500, they will receive an in-game notification, in addition to a "special icon next to their BattleTag, Gamer Tag, or PSN ID." Each of the platforms the game is available on (PC, PS4, Xbox One) will have their own leaderboard which are further broken up by region. This means Top 500 PS4 players from Asia will be different from Top 500 Xbox One players in China and so on.
Once a season ends, the leaderboards will also be reset. This means that players will have to work their way back up into the Top 500 every season. This is useful because it allows different people to be on the leaderboard at different times.

At the end of each season, anyone who made it into the Top 500 will receive a special, animated spray. This will not mean that you have to hold your spot on the leaderboards for a certain period of time. Any time you get there, it will count towards receiving the spray. To get a spot in the top, you also will need to be above rank 60 in Competitive Mode.
This isn't all that Blizzard plans to do with Overwatch's leaderboard. They also announced that, in the future, they will add a graphical leaderboard that will include the names and ranks of their top players. Perhaps this new system will give people more of a reason and reward to play competitive mode and perhaps take it more seriously. It remains to be seen what kind of effect this will have on both the game and the community.