Registration will open tomorrow (April 15th) for Rockstar Social Club - a new website from Rockstar featuring all kinds of multiplayer leader boards and stat tracking. Here are some of the features mentioned in the press release that was sent out on March 27th:

• LCPD Police Blotter - A virtual map and tracker of single-player criminal activity logged in Liberty City from the aggregated data of millions of connected players - showing the most dangerous areas of town, most commonly used weapons and more.
  
• The Story Gang - This special single-player leaderboard recognizes players who complete Niko Bellic's main story arc of Grand Theft Auto IV - The leaderboard ranks players according to the total amount of playing time it's taken to complete the story, as well as a historical rank by who has completed it first. Members of this club will receive special online widgets and merit badges marking all of their in-game accomplishments.
  
• The 100% Club - Watch to see who will be the first to complete 100% of the game. The first ten people to be identified on the Social Club as reaching 100% will be sent an ultra-rare commemorative 'key to the city' to mark their accomplishment. In the future, the 100% Club will then carry a historical leaderboard showing rankings of who has completed 100% of a game in the shortest span of playing hours.
  
• The Hall of Fame - This area will dynamically recognize those singularly elite players who have reached the top of the hill on various statistical leaderboards, and will also contain a personal awards display of special in-game landmarks and successes in Social Club competitions.
  
• The Liberty City Marathon - A ranking of special physical milestones achieved in the game - from the amount of miles walked, driven, or swam - to the number of bullets fired and stunt-jumps jumped. There will be additional special marathon-based competitions in the future from this area as well.

Rockstar say that additional features will be added to the website following the release of Grand Theft Auto IV, including competitions and challenges. You will be able to register with your Xbox Live Gamertag and/or PlayStation Network ID.

Link: Rockstar Social Club