Phoenix and Witherspoon have raised the bar for actors singing on screen. Actors can't get by anymore with having their voices dubbed by real singers, like Natalie Wood did in the screen version of "West Side Story."
"I don't think we're going to see a Natalie Wood scenario happen too much, unless the movie is going for a very campy kind of a feel," Vaccari said. "These days, I don't think people would go for that. The publicity backlash would be worse."
In Woody Allen's 1996 musical "Everyone Says I Love You," Drew Barrymore reportedly convinced Allen that her voice was too awful for even the "realistic singing voice" concept he was going for, and was the only one dubbed in a cast that included Julia Roberts, Edward Norton and Natalie Portman.
But when she played a songwriter opposite Hugh Grant in 2007's "Music and Lyrics," she bravely sang herself.
"She was tuneful and not completely embarrassing," Ann Donahue, senior editor at Billboard magazine, told ABCNews.com. "I think if it's an endearing part of the character, it's OK if it's not perfect."
"Sometimes you sacrifice a little of the singing if all the other areas are strong," Vaccari said.
Such was the case with the decision to cast Johnny Depp in "Sweeny Todd."
"He's a great actor. Sure, there are better singers. But I don't want to see Jon Bon Jovi play that part," Vaccari said. "I don't think there are a tremendous amount of options, people who can sing and are very bankable names."
"I don't think anyone is going to put someone in a Broadway musical if they can't sing. In a movie, it's a little different," Vaccari said. "There are things you can do to make it sound better."
Then there are some actors who so enjoy singing on screen that they decide to cut an album, often to mixed reviews and success. Lindsay Lohan's debut album peaked at No. 4 on the Billboard pop chart, but her second died quickly on the vine. Her third is due out in November.
Scarlett Johansson's first album was panned by some critics, but Donahue said it had a decent showing on Billboard's Heatseeker chart, which tracks albums that appeal to the college crowd.
"Some actors secretly know they shouldn't be singing, but they like the chance to try something new," Donahue said. "It's hard to do both and have a reputable career."
Donahue said she can only think of one person who excels at both singing and acting:Jennifer Hudson.