A study out of Granada University in Spain found that beer is a better liquid to replenish fluids after a workout than water. Beer retains fluid better than water and that the bubbles helped quench thirst and the carbohydrates made up for lost calories. Of course if you are working out to burn calories then, well, better stick to water.
The results don't actually surprise me because over the years beer always was a better hydrator after cutting grass on hot summer days than a glass of water. Felt better, bounced back from the heat better.