The problem I had was a soreness in my upper right arm and shoulder that came on about 2 weeks into my creatine use. At first I thought it might have been a mouse or keyboard repetitive motion problem, but I finally decided it was the creatine. Ron McBee had a similar problem. The soreness was bothering my running, so I quit. After a couple of weeks the soreness was gone, I lost 2 pounds and my upper body shrank back to its normal self.
Creatine is expensive, by the way.
I've tried this on a few long training runs. When I stopped the creatine, the weight and heart rate returned to normal. Given the high price and minimal to negative results, I'd say that creatine is of little value in endurance events. Lots of research supports the benefits of creatine for power athletes like lifters. I haven't seen any conclusive work on endurance athletes, though it may be out there.