Got this info from a company that sells creatine so take it for what its worth:
From Universal Nutrition:
Unless you have a pre-existing medical condition, creatine use should not damage your kidneys or liver. Most of the hype has been the result of anecdotal reports. In one study which tracked healthy athletes over a five-year period, football players who used creatine at levels up to 15.75g of creatine per day showed no effect on markers of renal or kidney stress. In another study conducted by Dr. Kerry Kuehl at the Oregon Health Sciences University in Portland and presented at the 2000 annual meeting of the American College of Sports Medicine, the kidney function of 36 healthy male and female athletes who consumed 10g of creatine per day was examined. After twelve weeks, Dr. Kuehl found that creatine did not adversely affect kidney function.
While creatine is non-toxic, creatine use is not wholly risk-free. As with all other nutritional supplements, individuals with pre-existing medical conditions should not take creatine or other sports supplements. For example, there have been at least one case study which reported kidney inflammation in subjects who used creatine. However, in one case, the patient had a pre-existing kidney problem.