Pittsburgh had their best day in a long, long time. The two top teams in the league just got dealt huge blows.
The Patriots' huge blow didn't change anything for the Steelers, who were already in the driver's seat for the #1 seed. The only change was that the Steelers no longer need to win out to get that #1 seed. This isn't necessarily a good thing. The motivation of having to win every single week is now replaced by the motivation of winning one more game to clinch, then rest. Good teams can lose their edge quickly. The only good news for the Steelers is that, if the Pats clinch the #2 seed and first round bye next week, they won't have much motivation to beat the 49ers in week 17, either.