If you sit there drinking nothing but coffee for a couple of hours you’ll burn off a couple of drinks worth of the alcohol you drank before and while your BAC will still be the same as if you had switched to plain water the caffeine will actually counteract some of the depressant effect of the alcohol and be slightly less impaired than if you had just switched to plain water. I bet this would bear out in a controlled experiment where we took two control groups, had them all drink the same amount of alcohol and then had one group switch to water and the other to coffee. Stimulants do help counteract some of the impairment caused by depressants.
I stipulated that caffeine will counteract some of the drowsiness caused by alchohol, but I wouldn’t want to count on the stimulant effect to save my butt if I were driving drunk (or after being up for 24 hours for that matter).
OK, I guess we have a dissenter. What the heck do I know?