We have managed to put our hands on Valve CEO Gabe Newell's Steam user name and passwords through the most unusual way: from his own mouth during a public GDC session.
Newell chose to reveal his personal Steam account detail in order to prove the strength of the newly announced Steam Guard and to prove that it is capable of protecting Steam user's account even if the attacker knew both the username and password.
There are still some issues concerning Steam Guard that hasn't been addressed by Valve. The most prominent of those issues is what happens if the user's PC stops working, or he upgrades his CPU or motherboard. However, Valve has promised it will "provide more information in the near future that should clear up some of these questions and the surrounding confusion."
Gabe Newell's user name is gaben@valvesoftware.com and his password is moolyftw