If the San Francisco 49ers aren't careful, they're going to wake up one day and realize just how much fun they missed out on this season.

Talk about a tight-lipped team that won't even allow itself to pat its own back after an impressive 8-1 start. The 49ers are drier than a martini when it comes to enjoying their success thus far.

Isn't this the same team that used to talk like there was no tomorrow? Didn't their players used to tweet out of control and issue friendly threats to their enemies, like the Cardinals, their opponent this Sunday at Candlestick Park?

These aren't those 49ers anymore. Maybe that's a good thing.

First-year head coach Jim Harbaugh has made it all about business these days. He's keeping his players' heads buried in the playbook and their mouths wired shut from creating any possible controversies or distractions.

"I think this team has really taken after that," quarterback Alex Smith said during a conference call Wednesday with Arizona reporters.

It may be boring, but it's working.

With a victory over the Cardinals, San Francisco would push its winning streak to eight games - its longest since 1997, when the team opened 11-1. Another win could put the 49ers in possible position to lock up the NFC West title the following week or two.

"We've got a lot to take care of before we can even talk about anything like that," Smith said.

See? Harbaugh's got his players so grounded that even the quarterback everybody used to love to hate can't enjoy himself.

The 49ers have put themselves in contention for home-field advantage in the playoffs primarily because of an outstanding defense, which has allowed the fewest points (138) and forced the most turnovers (21) in the league.

They haven't allowed a 100-yard rusher in 31 consecutive games, and this season haven't given up a single rushing touchdown. You'd think Harbaugh would be gloating over that, but he isn't.

"I can't take any credit for that," he said flatly. "I don't help block or tackle anybody."

Quick, somebody please give this guy a happy pill or something. Pressed to at least try to heap some praise on his defense, Harbaugh paused and thought about the question for a moment.

"Um, I'm very happy with our defense," he said. "Just how well they're playing together. They're playing great team defense. They're playing within the framework of the defense."

Wait until you hear what he had to say about the evolution of Smith, who had been so inconsistent in his career that the 49ers were on the verge of releasing him before bringing in Harbaugh.

Smith has been ultrareliable in 2011, completing 64 percent of his passes, good for sixth in the NFL. His 95.8 passer rating ranks seventh. He's thrown for only 11 touchdowns, but his three interceptions are the fewest of any starter with at least 200 passing attempts.

Why is he suddenly so much better?

"We don't have an answer for you," Harbaugh said. " . . . We're more consumed with asking questions than we are answering things."

Huh?

"Are we good enough to keep winning, finding ways to win? Are we disciplined enough to keep studying? Are we smart enough? Are we competitive enough? Are we strong enough?"

Well, they certainly are bland enough, at least to hear them talk. Smith, at least, says he's no longer trying to force plays and he's quit trying to "put games on my shoulders." He got that, he says, from Harbaugh, the former Michigan and NFL quarterback.

But how did Harbaugh manage to get the 49ers to 8-1 without the benefit of a full off-season? Especially when it seems like every other team that hired a new coach or coordinator, or is starting a new quarterback, has struggled?

"Yeah, yeah, I don't have an answer for you," Harbaugh said. "As it relates to us, we're really not living in the past."

Seriously, who stole this guy's lunch?

Smith was asked whether he's having any fun rolling up the victories.

"Anytime you're winning and having some success, you expect it to be more fun," Smith said. "But beyond that, Coach has done a real good job about just keeping it about football."

It's the NFL. For Harbaugh and the 8-1 49ers, that may stand for the No Fun League.