She: Where'd you learn to dance like this?
He: Ballroom dance class.
She: Oh! You're gay.
He: The gayest.
[Pause]
He: No, no. My mother took me when I was 8. She wanted me to be Fred Astaire. I wanted to be Marcus Welby.
She: Mm. So now you're a little bit of both.

There's a masterful economy of flirtation, uncertainty and mutual seduction packed into that single minute of screen time. When it begins, Mary and Steve are just two strangers fooling around. When it's over, they're falling head over heels for each other. McConaughey isn't necessarily a better actor than Lopez, but his languorous country-boy good looks are a nice match for her Catholic-girl sweetness. When you see them together, you can immediately envision them wearing matching pajamas and sharing the Sunday paper.

Of course there's a problem, and it has to be a doozy to interrupt this blossoming love affair. The next time Mary sees Steve, he's being introduced to her as "Eddie," the fiancé of one of Mary's clients, a blond, brassy and bronzed rich girl named Fran (Bridgette Wilson-Sampras). We're at ballroom dance class, of course, and Fran, suspecting nothing, sends Eddie and Mary onto the floor while she takes a phone call. They reprise their earlier slow dance as a hilarious comic-erotic tango -- both Lopez and McConaughey are dexterous and agile dancers -- while Mary quietly spits venom: "What I'm thinking about," she murmurs to him, "involves a machete and a pair of pliers."

There's a reason dance is used so effectively in "The Wedding Planner": Director Adam Shankman is a longtime film choreographer whose credits stretch from "Mission to Mars" to "Boogie Nights" to "Weekend at Bernie's II." But after this high point in the dance studio (which features an enjoyable cameo by comic Fred Willard), the movie slides into a long groove that is enjoyable enough but adheres to formula every step of the way. Naturally Steve/Eddie has an explanation for his apparently outrageous behavior, and naturally Mary doesn't want to hear it. Out of professional pride Mary refuses to give up Fran and Eddie's wedding, and the oblivious Fran keeps coming up with reasons to strand the duo together, saying blithely, "I trust you guys."

There are amusing gags about how a wedding planner can tell a marriage is going nowhere ("I Honestly Love You" by Olivia Newton-John is a key indicator) and an unrewarding subplot about Mary's father (Alex Rocco) and the buffoonish Sicilian immigrant (Justin Chambers) he hopes to set her up with. There are random comic bits involving Fran's rich and boorish parents and a limestone penis that winds up in Mary's purse. Shankman doesn't take much advantage of shooting in America's most photogenic city, but he faithfully keeps things moving toward the collision of implausible circumstances that will set all the movie's wrongs right. In fact, the denouement of "The Wedding Planner" is far clumsier than what has gone before, but even that failing can't cast a shadow on this whimsical, low-calorie treat.

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