On his first carry against the Eagles in the Wild Card game, Green Bay Packers RB James Starks ran for 27 yards. Mike McCarthy kept giving him the ball because he went with the hot hand. Who knows what would have happened if he hadn't gotten off to that hot start. It's possible he could have been left inactive the next couple weeks. Instead he's had 70 carries so far in the playoffs.
While he was good against the Eagles, he's been lousy against the Falcons and Bears. However, I can really appreciate that he hasn't had a single fumble in the postseason. But 2.6 and 3.4 yards per carry are stats that can drag an offense down. In his defense, the Packers rushing attack overall was poor against both teams. The Falcons run defense was even better against the Packers during their week 12 regular season game, and the Packers haven't run the ball very well against the Bears over the past three seasons.
The bad news is that Steelers run defense is arguably the best in the league. If Starks couldn't run well against the Falcons or Bears, he's not likely to get it going in the Super Bowl. But there is a case to be made to keep running the ball. Kevin Seifert posted a quote from QB Aaron Rodgers, who pointed out that the play-action game has been better during the playoffs due to the threat Starks poses.
And another point I would make is that it's easy to give up on the run game, but you never know if that next carry is the one that goes for a big gain. It's easy to see that Starks is the most talented rusher currently active on the team. The threat he brings with his big play potential, and the help it provides to the passing game, makes it worth their while to keep grinding it out on the ground.