Like it or not, when it comes to Hollywood star power it's all about the fans an actor or actress can bring to theater seats.

And the millions he or she can make them shell out at the box office. With the disappointing third-place, $20 million opening of .

''Knight & Day'' last weekend, questions are being raised whether Tom Cruise's personal appeal and the ability to ensure a huge opening weekend have begun to wane.

Cruise and 20th Century Fox, which released ''Knight & Day,'' went out of their way to promote the movie as a major summer blockbuster. The actor and co-star Cameron Diaz -- herself in need of a major hit -- seemingly were everywhere in the crucial weeks prior to the June 25 opening.

Cruise and Diaz not only did the usual morning and late-night talk shows, but they even participated in an expensively produced European press junket in Salzburg, Austria, and Seville, Spain, where they joined in the re-creation of ''Knight & Day'' action stunts with TV reporters from smaller markets.

''I can't believe it,'' a veteran TV entertainment reporter told the Sun-Times. ''Back when 'Jerry Maguire' came out, I couldn't even get invited to that press junket held over Thanksgiving weekend -- and Tom Cruise was too important to even participate! Now I'm racing around Seville with him and a stunt motorcycle specifically for my station.

"You figure he realizes he can't take us for granted anymore. He's got to sell his pictures. Audiences aren't exactly lining up for him the way they used to.''

Chiming in with a similar sentiment, a longtime Hollywood studio publicist said admiringly, ''You can't say Tom and Cameron didn't do everything they could to promote and sell that picture. Yet, it did seem almost a bit desperate -- perhaps anxious is a better word -- to describe how hard they pushed the film.''

As has been his preference since his younger days, Cruise, who turns 48 on Saturday, insisted on pushing his body to create action sequences for "Knight & Day," where many of his contemporaries would have demanded stunt doubles.

''The guy's phenomenal,'' said ''Knight & Day'' director James Mangold. ''His talent, his amazing love affair with the camera and his true star quality -- something that continues as strong today as ever -- make him an enduring movie star for a long time to come.''

To be fair, the marketing of ''Knight & Day'' was confusing -- including the lack of Cruise's or Diaz's instantly recognizable faces on the movie's posters. Fox co-president of marketing Tony Sella, clearly concerned about Cruise being targeted for the film's lame launch, told the L.A. Times, ''Blame me, don't blame Tom Cruise. We did lots of focus groups for this film, and no one ever said there was a star problem. Never. Tom Cruise was not the issue.''

Perceptions of Cruise took a curve after a string of unusual behavior in 2005, including his rapid courtship of and engagement to Katie Holmes, his couch-jumping appearance on "The Oprah Winfrey Show" and his criticism of former co-star Brooke Shields for using anti-depressants.

Looking back on the actor's box office track record since then is a tricky exercise -- given his eclectic role choices.

His greatest success in the past five years came with the ''War of the Worlds'' remake -- which chalked up a very respectable $234 million domestically after its release in 2005. While critics dubbed ''Mission: Impossible III'' the best in the series so far, audiences only chipped in $134 million in 2006 -- still a number in solid territory.

Though Cruise starred (along with Meryl Streep) in ''Lions for Lambs'' in 2007, that $15 million bomb should be placed in co-star and director Robert Redford's lap. By the same token, even though ''Tropic Thunder'' was a surprise $110 million hit in 2008, Cruise's small and barely recognizable role as movie producer Les Grossman doesn't exactly give him the right to claim box-office gold for that one.

To build buzz for "Knight & Day," Cruise returned to the Grossman role for dance duet with Jennifer Lopez at last month's MTV Movie Awards. ''While Tom clearly had fun with J. Lo and loves that character [which he'll reprise in a 'Tropic Thunder' sequel], it did make me wonder whether we would have seen the old Tom Cruise -- back when he was the biggest star in Hollywood -- doing shtick like that? I don't think so," said a major Hollywood executive, who declined to be identified fearing Cruise's displeasure could cost him a future career opportunity.

"He's at a point where he realizes he needs to do whatever it takes to keep himself in the public eye,'' the exec said. ''I think that's why you see him and Katie trotting out their kid [daughter Suri] every chance they get. Sure, they're cute photos of a very attractive and seemingly happy couple, but it's also to remind the public, 'Hey! I'm still here! I still look good!' ''

Given that ''Knight & Day'' opened just a few days before this week's explosive bow of ''Eclipse,'' the third film in the mega-successful ''Twilight'' franchise, the questions arise: Are Tom Cruise and Cameron Diaz too yesterday? Had they already reached the pinnacle of their star power by the late '90s or early '00s? Are they able to appeal to the current crop of 'tweens, teens and early twentysomethings who largely drive box-office numbers?

One of Cruise's closest associates, who requested anonymity because he had not received permission to speak on the actor's behalf, shrugged off those concerns. ''Tom Cruise is still a hugely popular star with audiences of all ages, including kids. I think when 'Mission: Impossible 4' comes out next year, you won't be asking these questions about Tom Cruise's career being finished. 'Knight & Day' is merely a detour -- certainly an expensive detour for the studio, but no indication Tom's career has lost its luster.''

That source hastened to point to Cruise's 2008 film ''Valkyrie,'' about the failed attempt to assassinate Adolf Hitler. ''So many people ridiculed that film. The Germans made filming there a nightmare because of their issues with Tom over his Scientology. Critics were skeptical -- until they saw the movie. And yet, 'Valkyrie' ended up doing something like $80 million domestically [$83 million, to be exact] -- and at the time, everyone was carping about how this was going to be Tom's downfall.