What happens in Vegas depends on what you're watching: it's murder ('CSI'), Armani suit modelling ('Oceans 11'), bad acid trips ('Fear and Loathing?'), or not much (that dull 'Las Vegas' series). In the new love-in from Ashton and Cameron (no surnames necessary if you're basically portraying yourself) it's all good: getting drunk, getting hitched, and getting lucky to the tune of $3-million.

It?s what happens outside Vegas that's the problem ? as the hangover kicks in, so do the romantic comedy conventions. When Camer? uhm? Joy McNally (Diaz) and Jack Fuller (Kutcher) wake up after their one wild night, the relative strangers agree to get the slurred marriage vows annulled. There's just one problem: the wedding-worshiping divorce judge won't hand over their jackpot winnings unless they make the relationship work for six months.

Of course, with romcoms as predictable as underdog-sports-team-comes-from-hopelessness-to-win-the-championship films and new-school-teacher-inspires-troubled-kids movies, it's no surprise where this is headed. The couple, who settle in Jack's apartment, aren't exactly compatible when sober: he's a recently unemployed slacker not averse to putting popcorn down his pants, she's a highly-strung control freak just dumped by her long-term boyfriend.

But the 'You, Me and Dupree' premise is soon replaced by the open warfare of 'The Break-Up': when both partners realise they can get out of the deal if the other cheats or misses their court-ordered counselling sessions, the schemes come thick and fast. And yet, while they?re bickering over the bathroom (Kutcher's sink technique is quite impressive) or sending sexy strippers over to lead hubby into temptation, the 'Odd Couple' realise they might just maybe, perhaps be made for each other. It?s the romantic comedy formula, virtually unchanged since 1933 when King Kong first kidnapped blonde beauty Ann Darrow.

And yet, despite even falling into the trap where the quirky best friends have a far more interesting relationship than the leads ('Failure To Launch'), 'What Happens In Vegas' has something that?s missing from most cynically mass produced Hollywood fare: a real sense of fun. With the stars clearly slumming it (Diaz' performances haven?t changed since 1933; Mr Demi Moore seemingly chosen for his experience with older women), they're content to just have a good time. It's simply infectious.

When coupled with another break with romcom convention (a real connection between Ashton and Cameron), this inconsequential little love fest is less of a gamble than hitting the blackjack tables on the Strip.