Hey, all you groovy night owls: Look for Simon &#038 Garfunkel to perform together on The Late Show with David Letterman this Friday. It's their first public gig since they sang at the Grammys in February, when they snagged a lifetime achievement award. As reported yesterday, the duo's 32-city reunion tour — their first tour in 20 years — kicks off Oct. 18 in Auburn Hills, Mich.