Halo 2: 4.75m gamertags
670 million games played.
If you were in any doubt about how much of Xbox Live's popularity is down to Bungie's legendary Halo 2, consider the following statistic: at the point of scrapping its old recording system recently, Bungie had logged 4.75 million gamertags, out of around six million Xbox Live subscribers.
The number of games played is now almost 670 million, with (in case you're interested) 4.5 billion slots filled across those games, suggesting that the mean Halo 2 game was contested by around seven players. (That also explains the confusing "4.5 billion played" stat we remarked on in November - they meant slots filled.)
In case you're (still) interested, that 670 million figure means that around 170 million games have been played since the start of June 2006, when Bungie revealed it had passed the big five-oh-oh-oh-oh-oh-oh-oh-oh. It's the sort of success they will be hoping to repeat with Halo 3, due out on Xbox 360 later this year - and one of the reasons they have relaunched Bungie.net in prettified form this week.