If you really want to know the closest thing to an upset the Steelers will have, watch the Pitt/Baltimore game. Baltimore will be fighting to keep their wildcard shot, and Pitt will be fighting for homefield. Emotions will be WAAAY high, so it'll go either way.
Want an upset this week?
Cincinnati over Baltimore. People keep turning their backs to Cincinnati. Yeah, the offense won't do much against the Raven D, but the Cincinnati defense has been very opportunistic against its last few opponents (the browns game being a mulligan). I think that if they can stop Chester Taylor (Jamal already told everyone he isn't playing), they won't have trouble picking off Boller. This Cincy secondary is one of the tops in the NFL (the line and LB core, though, are questionable at best).
Don't like that upset? How about Brett Favre getting his revenge on the Eagles this week? Yeah, the Pack are just in a groove, especially after last weeks win.