If you think the preseason means something, you need to learn the game.
The 49ers are historically bad in the preseason. I see a lot of "Faithful" bailing on the season because they don't look good in the preseason, and to them I say good riddance. These people are called homers.
Here's the thing.. With all the new starters on defense, it's gonna take time to get it together. It'll be a few games (full games) before that D starts playing to their potential. Or did you guys forget about the '94 Niners already? Their D was ass until they started to mesh. Our offense looks fine, even in the preseason, without Frank Gore. The only time they looked bad was against Chicago, and that was a run-heavy game. They didn't even give Alex a chance to pass because Nolan wanted the running backs to show what they've got. Not only that, but you need a gameplan to beat Chicago's defense because it's so good, you will never see that in preseason.
I laugh at these people who are worried because of preseason performance. If the team looks like this after the 3rd or 4th game, then it's time to panick.