And she said the current trend toward multiple careers applies to celebrities as well.
"Younger people in particular just don't see the merit of 'paying their dues,'" Jansen said. "It's easier and more acceptable to make job and career changes now. This is because of technology and the myriad choices we can make regarding work. The media glorifies people who try different things."
But while he admits it's more widespread, PR guru Howard Bragman doesn't see this trend as anything new.
"Madonna's writing kids books, 'The Hills' girls have clothing lines, Ashton Kutcher has a bunch of restaurants," said Bragman, who owns L.A.'s Fifteen Minutes PR. "These days, everyone is everywhere. But I don't think it's a new phenomenon, actually. Historically, a lot of famous people have had other interests. Frank Sinatra and Big Crosby crossed from acting to music with equal aplomb."
But with the level of media saturation today, celebrities have more eyes on them than ever before -- and, therefore, bigger marketing power. "We live in an age when each celebrity is a brand, an image, a point-of-view -- and celeb-watchers become a loyal audience," said Bragman, whose book on celebrity, "Where's My Fifteen Minutes?," is due early next year.
"So people want to expand their brands, use that reach, they can command that attention," Bragman continued. "A lot of times, it's about the money. Usually, an outside company comes to you to license your brand. People are throwing money at these stars to open that restaurant or record that album. If they want to do a Paris Hilton line of shoes, they pay her to put her name on it and she has a bit of say over what they look like, how much she'll promote it and so on."
This is especially true with record deals thrown at celebs like Johannsson and Hilton.
Paris Hilton debuted an album, "Paris" in 2006.
"There's a lot of talk about brand-building," said Billboard's Cohen. "There's money being thrown at these people to do whatever they want. Take Paris Hilton -- her album was actually the least embarrassing thing she's done so far -- it got decent reviews. But it didn't get taken seriously. And in Scarlett's case, someone at Atco records approached her and said, 'Hey, do you want to do an album? Here's some money.' That's pretty hard to resist."
Whether it was for money or artistic expression, Johannson set out to create a serious album. "It comes as no surprise that her foray into pop music eschews the Lohan-esque," said Blender magazine critic Jody Rosen. "In fact, it's hard to imagaine a record better calibrated to strike the chords of sophistication and credibility.
"Scarlett was very smart about this," said Cohen. "Tom Waits is an icon in the indie world. And the CD was produced by Dave Sitek, which Scarlett hoped would up her indie credibility."
Nonetheless, Blender's Rosen was not impressed. "You keep waiting for her to inhabit the songs, to read the lyric sheet like she would a script and get into character," she wrote. "As sometimes happens in Hollywood, it's simply a case of poor casting."
But, for some celebrites, what the critics will think takes a backseat to their desire for creative expression.