Somewhere, two copywriters from R&R Partners (the ad agency responsible for the initial promotion) are laughing -- all the way to the bank. Their phrase "What Happens in Vegas," now so ubiquitous, has successfully been plastered onto an often funny film that actually lives up to the spirit of the campaign.

Silly, wild, musical and brimming with folks who take chances, the movie mocks those who marry in Vegas, but also raises the question: Do they actually stay married?

Aptly named Joy (an ebullient Cameron Diaz) works on Wall Street and shares a killer apartment with her unappreciative fiance -- who suddenly dumps her. Meanwhile, Jack (an impish Ashton Kutcher, who at 30, here appears and behaves more like 23) is enjoying life as a rowdy, carefree bachelor and is routinely assured he's not exactly "serious boyfriend or marriage material."

Fired by his own father (Treat Williams in a scene-stealing, sincere performance), Jack decides to take off for Las Vegas with best friend Hater (Rob Corddry), a party pal who thinks three seconds after saying whatever comes to mind.

When her best friend (Lake Bell, in a drab role whose forced fun appears at times unnecessarily juvenile) asks a depressed Joy, "Where can you go to forget your troubles and act like a total idiot?" they agree immediately: Vegas.

Mistakenly assigned the same room -- great free publicity for the Bellagio -- Jack and Joy initially do not have a cordial relationship. But after they drown their sorrows at the bar together and wind up married, things get a bit complicated. While both are convinced they can easily wiggle out of the wedded bliss, there remains a major obstacle: the huge slot-machine jackpot, which now legally belongs to both of them.

A staid, smarmy Dennis Miller is brilliant as the no-nonsense judge who refuses to annul and sentences the couple to "six months of hard marriage." And just to make sure both parties genuinely make an effort, they are assigned a therapist: a not easily fooled and marvelously understated Queen Latifah.

With sobriety and forced close quarters comes the realization that "We can really talk," and talk they do. When Jack glibly dismisses marriage as an "outdated concept," the recently burned Joy has also grown a bit skeptical.

Each is outrageously stubborn and there are arguments aplenty, which their therapist views as evidence they're beginning to resemble a real married couple.

Brimming with physical comedy, some gross antics and a whirlwind of high-energy nightlife, this sentimental and occasionally sappy Vegas vacation adventure actually proves life-changing for both: Joy is no longer the uptight planner whose job overtakes nearly every aspect of her life. And Jack -- much to his father's surprise -- finally sees a project through to completion and controls his often distasteful, immature domestic ways.

Neither is exactly sure what to make of their gradually fading distrust.

Or as Jack ultimately realizes: "What happens in Vegas, you pay for when you get back home."

Far from believable, the romance here is more fluff than plot. But it's just enough to make audiences want to play the odds, blow on the dice and take a chance on someone new.