While Rascal Flatts enjoyed top billing for Monday night's Marcus Amphitheater show at Summerfest, it was hard to tell how much of the crowd was there for them, and how much of it was for the opening act, teen sensation Taylor Swift.

(In the interest of full disclosure, I did not know who Taylor Swift was before the show. I was under the mistaken impression she was a product of the "American Idol" machine.)

After watching the entire crowd -- including the three 'tween-agers in front of me standing on their chairs with their Taylor T-shirts and pink digital cameras (who filled me in on Taylor's bio after her set) -- rise to its feet when the 18-year-old burgeoning star was introduced, I realized the boys who sing "Bless the Broken Road" and "Life Is A Highway" might not have been the sole reason ticket brokers were getting $500 or more for prime ducats before the show.

"This is a song I wrote in ninth grade for a talent show," Swift, clad in a sparkly sequined sundress, informed us non-Taylorites before belting out, "Our Song," her first No. 1 hit.

It elicited a "We love you Taylor!" in-unison squeal from my obstructed-view seat creators, who also waved at Swift a half-dozen or so times during her 45-minute set.

Later, Swift sang "Should've Said No," a song about "a guy who cheated on me" and shouldn't have "because I write songs" and his infidelity is now a matter of public musical record. The grudge-songwriting quickly became a theme.

The line "You should've said no, and you might still have me," seemed to resonate with the youngsters in the crowd, despite their presumably limited exposure to relationship problems. Swift's drumming on upside-down metal trashcans with her fiddle player also went over well.

Swift, who lives with her parents, Scott and Andrea, and her brother, Austin, in Hendersonville, Tenn. (or so I learned from Wikipedia during the show), also sang "Tim McGraw," her first single, during which she requested her fans wave their illuminated cell phones overhead.

I was too busy writing this review on mine to participate, but the high-pitched woo-hooing that followed was deafening, and Swift admitted she "didn't know what to say" after the outpouring, before adding, "I love you so much." I think she really meant it. No, really.

Then, she segued into her final song, "Picture to Burn," by saying, "Before I go, I want you to know I try to be a nice person. But if you break my heart or hurt my feelings ... or mess with my friends from Milwaukee, then I'm going to have to write a song about you."

All I could think about was how thankful I was that none of the women in my past are songwriters. Well, that and how odd it was that Swift's guitarist and banjo player were sporting Flock of Seagulls haircuts.

While Rascal Flatts' road crew was setting up, I asked 12-year-old Halle, 12-year-old Katherine and 11-year-old Emily -- three friends from suburban Chicago who came with Emily's parents -- what they liked about Swift.

"I like that they don't remix her voice at all (during the show), and I like her boots," offered Halle, while Katherine pointed out that Swift "makes awesome songs." Emily called Swift her "favorite artist," in part because "she's really pretty."

"We won't stand on our chairs for Rascal Flatts," Halle promised.

That turned out not to be entirely true, and Rascal Flatts -- the act I'd come to see, as did Emily's 8-year-old brother, Chris (with his cartoon T-shirt of the band) -- took the stage somewhat quickly after that, opening with "Still Feels Good" following a jarring pyrotechnic explosion.

"Life Is A Highway," a remake of the 1991 Tom Cochrane tune for the Pixar film "Cars," followed, a hit with the younger demographic.

Several slow tunes came next -- one of the inherent drawbacks to Rascal Flatts shows for those who prefer their more upbeat, concert-friendly stuff -- before "Stand," a 2007 No. 1 hit.

Overly chatty bass player Jay DeMarcus then launched into an annoying, interminable soliloquy about the scantily clad women of Summerfest, an unwelcome interruption that killed the momentum of an otherwise solid show. Lead singer Gary LeVox and guitarist Joe Don Rooney were less verbose during their turns at the mic throughout the show.

When the music mercifully resumed, "These Days," the band's first Top 30 hit in 2002, was the selection, followed by the 2006 No. 1 hit "My Wish," 2007 No. 1 "Take Me There," and the depressing cancer-themed "Skin," which was truncated as the band segued into an abbreviated "Feels Like Today," which deserved to be done in its entirety.

The rocking "Fast Cars And Freedom" re-energized the sellout crowd, and the conclusion of "Broken Road" led to the loudest ovation of the show.

"Here's To You" and "Bob That Head" closed the show, with balloons and confetti cascading down from above, before a solid encore featuring the humorously self-deprecating country-music send-up "Backwards," "Me And My Gang" and a cover of "It's Only Love," which fittingly included Swift's return to the stage before the "Good Night, Y'All" drape dropped and the house lights came up.