: Put a +1/+1 counter on each artifact creature you control.
"The world is already run by all manner of machines. One day, they'll remind us of that fact." —Sargis Haz, artificer
Official Rulings for Steel Overseer
8/15/2010 : Steel Overseer is affected by its own ability (assuming that, by the time the ability resolves, you still control Steel Overseer and its types haven't changed). You'll put a +1/+1 counter on it, as well as on each other artifact creature you control.