It wasn't really his fault, that's not his regular gig and he was trying to make the big play when the coaches should have stressed ball security first. His big kickoff return looked like a fumble waiting to happen, too.
The 49ers played their game today and when a few bounces go against you (4 fumbles that mattered with 3 recovered by the Giants plus another just a second too late, plus two easy interceptions missed when Goldson ran into a teammate) with that style of play it's really easy to lose. I don't think Smith was much different today compared to last week, the offense had long bad stretches, then too. He just missed a few throws (like Manning did) that he made last time. I would have liked to have seen more running plays in the fourth since that seemed to be working pretty well, but otherwise there isn't much to complain about.