Cameron Diaz, perpetual motion machine. The "Shrek Forever After" star is booked solid this summer, finishing up the raunchy comedy "Bad Teacher," appearing as a presenter for the 2010 MTV Movie Awards on June 6, then promoting the action comedy "Knight and Day," opening June 25 with her co-star Tom Cruise.

As she makes her fourth and final turn voicing Princess Fiona in Dreamworks' animated fairy tale, Diaz admitted that sometimes her career seems like something out of a Cinderella story.

"I'm pretty blessed, absolutely," she told me in a phone interview. "It doesn't go unnoticed by me that I pretty much live an extraordinary life. It's amazing." Like all good folktales, it has a moral, she said.

"The moral is to appreciate everything you have. If you appreciate what you have, you're in need of nothing else. And also to love what you do and to put out into the world what you want to get back."

Spoken like a true princess. Diaz said she's truly sorry to be saying farewell to Fiona. Not only did the role make her Hollywood's highest-paid actress, she considers the ogre a good role model for girls.

"She's never depended on anyone to rescue her, which is a different message from Snow White and Rapunzel, waiting for a Prince Charming to come rescue her. She was capable of getting out of the tower herself. She definitely took on Shrek as her partner rather than as her rescuer."

That do-it-yourself ethic has fueled Diaz's bustling career. While she doesn't boast the range of a Meryl Streep, she moves easily from lowdown comedies to heavy drama, action romps and romances. They haven't all been critical or popular hits, but Diaz doesn't disown any of the choices she's made.

"I don't think any choice is a bad choice. Whether or not the film is successful in the box office or not, I feel like every opportunity I get to work and make films, collaborate and learn, is an awesome opportunity, and I'm grateful for all my experiences. Everything I learn from one film I can apply to the next and the next.

"Working with smart, talented people with great ambitions is the way to go. If you can latch your trailer onto that truck, I say do it."

In her next films, Diaz returns to familiar territory, playing the reluctant sidekick of superspy Tom Cruise in "Knight and Day" and the demure love interest to comic-book crime fighter Seth Rogen in "The Green Hornet."

"It's fun to blow [stuff] up," she said with a hearty laugh. "That's why they make so many movies that that happens in. Telling extraordinary stories that would never really happen in real life, that's the fun of moviemaking. It's escapism every time. Even if it's in a drama that you relate to emotionally, it still takes you out of your life and involves you in somebody else's story."

In addition to her acting fame, Diaz has become a prominent environmental advocate, traveling the world as host of MTV's eco-education series "Trippin'." She noted that a central theme of the final "Shrek" story is "being appreciative of what you have. It can be fleeting and easily taken away. You have to protect what you have and value; it can't just be taken for granted." The same goes for earth's ecosystem, she noted.

"We all rely on one another for the health of this planet. If the world's environments aren't all thriving, they're all failing. That's what we were trying to emphasize to the crowd that watches MTV," which leveraged her celebrity to draw viewers to an informative nature series they would probably otherwise shun.

"You want to put your energy into the right place. You can't shift the needle if the layman doesn't have the language to understand the issues. It's a huge challenge, but it's obviously a worthwhile cause because it's the only thing that connects all of us, the only thing the entire population of the planet has in common." Dealing with the myriad threats of pollution, species loss, global warming and the rest is a long-term mission with no magical happy ending, she said.

"I don't believe in happily ever after. It ain't over till it's over, and I'm not looking for that to happen any time soon!"

Colin Covert • 612-673-7186