Crash diets don't work, kids
 

Fun & interesting read: http://www.topgear.com/uk/photos/how...car?imageNo=12

In a nutshell: Just loosing weight off your car may not net the performance gain you hoped for unless you invest in some chassis tuning to re-balance the car.

Well depends on what you are measuring, I'm sure if they just measured pure straightline performance it would be hard to deny that losing 10% weight to increase your power to weight ratio would only help. If it really upset the car balance that much then I suppose it's possible to lose enough cornering traction. In most cases a good corner balancing session with a decent set of coilovers should turn that around, especially if you can adjust spring rates, shocks, and front to rear balance.