Take a look at this article ... it explains everything.
http://www.straight.com/article-213828/britney-spear-brings-lipsynched-circus-vancouver
If you don't want to click the link to another page, here it is behind the cut:
Britney Spears stuns Vancouver fans with demand to stop smoking pot
By John Lucas (Georgia Straight)
At GM Place on Wednesday, April 8 2009
Well, that was weird. I can honestly say I’ve never been to a stadium show by a major touring act that ground to an utter standstill after just a couple of songs, but that’s precisely what occurred when Britney Spears appeared at GM Place.
What made it even more glaring was the fact that the star was given a buildup so mythopoeic that Jesus Christ himself would be well advised to take notes if he has a comeback tour in mind. After 15 or so minutes of presentable but not stellar juggling and tumbling by members of Big Apple Circus and a video introduction by professional bitch Perez Hilton, Spears finally appeared, appropriately enough, to the tune of “Circus”. Attired as a ringmaster (or at least what a call girl might wear if you paid her to dress up like one), a whip-brandishing Brit-Brit descended from the rigging on a platform to join her dancers, some of whom wore lucha libre masks and PVC briefs, while others looked like the kind of clowns that make kids piss their beds.
The Mexican-wrestler dudes pushed a writhing Spears around the stage in a gilded cage during “Piece of Me”, while hidden fans blew her platinum-blond hair extensions around. The rest of the show seemed destined to carry on in a similar vein-with Britney being rolled about on various circus-themed props while her dancers did all the heavy lifting-but then darkness fell.
The lights went down, the speakers went silent, and we waited. And waited. After a few minutes, the murmuring crowd grew louder, and speculation ran rampant. Was Britney coming back? Was she still in the building? Had she perished in the wake of some horrific wardrobe malfunction? Then the curtain came up, but there was no one on the stage. A nervous-sounding female voice-not Britney’s!-came over the public-address system to inform us that the show had been stopped due to inordinate amounts of cigarette and marijuana smoke in the air: “The performance will not continue until the air clears.” According to a statement posted later on Spears’s official Web site, “Crew members above the stage became ill due to a ventilation issue.” Fair enough.
After a 25-minute gap, during which listless audience members resorted to doing the wave to stave off butt-numbing boredom, the concert started up again as suddenly as it had stopped. Illusionist Ed Alonzo sawed Spears into three pieces and then made her disappear. She came back, but the Big Top conceit fell by the wayside when homiez on pimped-out low-rider tricycles arrived to provide the star with yet another prop to ride around on during “Boys”.
Spears did very little that could even charitably be described as dancing. When some conveyance or another wasn’t relieving her of the need to move under her own steam, she mostly just strutted about the stage, almost invariably clad in something that barely covered her ample ass cheeks. And a lot of the time she wasn’t there at all. During the seemingly endless costume changes, we were treated to such transparent time-fillers as martial-arts demonstrations, dance solos, and-most surreal of all-a video of Spears mouthing the words to Marilyn Manson’s version of “Sweet Dreams (Are Made of This)”.
You could tell she was lip-synching in that case because her mouth was moving while someone else’s voice was coming out of the speakers. Mind you, even when her own voice filled the stadium, that was no clear indication that Britney was actually generating the sound. I became convinced that her headset microphone was merely a prop, a speculation that was all but confirmed when she spoke for the first time all night-into a handheld mike, which she also used when an oversized parasol lifted her into the air during the ballad “Everytime”.
"Don't smoke weed!"
Either that was one of the few times she genuinely sang during the concert, or she’s just really damn good at sounding exactly like her records. I’m leaning toward the former, but what does it matter? No one dropped $125 to hear her sing anyway. The masses gathered at GM Place paid for the privilege of being in the same room as the former Mouseketeer. They wanted spectacle, and they got it, even if the woman at the centre of it all seemed oddly absent.
The Guardian’s Michael Bracewell once described stoic Pet Shop Boys keyboardist Chris Lowe as “possibly more famous for not doing anything than almost anyone else in the history of popular entertainment”. I wonder if Bracewell has ever been to a Britney Spears concert.