In the boulevards outside the O2 Arena, an already half-forgotten Big Brother winner skips happily past me, trailing screaming girls in his wake. Inside, young girls in Rihanna T-shirts and tutus link arms, showing pop devotion's more appealing side. Both sights are more memorable than Rihanna's actual show, which celebrates the 10 weeks at No 1 for "Umbrella" with an overblown yet old-fashioned spectacle.