Interesting debate on the need for protein during exercise in this month's Medicine & Science in Sport and Exercise.
There is presently no convincing scientific support for the contention that protein be included in CHO-based sports supplements -James Betts
Several studies have investigated the effect of consuming protein with CHO compared with CHO only during prolonged exercise. Ivy et al. (13) reported a 36% improvement in time to fatigue after 3 h of variable-intensity cycling when cyclists ingested a mixture of CHO and protein compared with a matched quantity of CHO. -Emma Stevenson
Who is right? Read the entire debate here. I think we can safely say that a protein/carb mix is an effective recovery drink, however there isn't much to support that protein taken during activity will enhance performance. That does not mean it won't help speed up recovery and ultimately allow the athlete to perform at a higher level-
"although the benefits of consuming a CHO-protein mixture during exercise on immediate performance are still uncertain, this nutritional strategy can have a positive effect on the recovery process and therefore may improve exercise performance on subsequent days."