[noobie]

*of a user's activity

[kqr]

...of a user's public activity.

[ben174]

Also, only commits to a master branch, for some very odd reason.

[mathieuh]

Contributions to private repos are also taken into account.

[Cthulhu_]

Only if you're logged in; not sure if the status is visible if you're part of the same team. (look at your own profile in an anonymous browsing window, if you contribute to a private repo)