Warfarin sensitivity is one of the more concrete useful things to come from being tested. I, for instance, have a genetic increased sensitivity to it and knowing that makes me feel better in case I ever need it. Apparently I also have substantially increased odds of liver toxicity from the osteoarthritis drug Lumiracoxib. Not immediately useful, but good to know. Currently 23andMe lists 20 drug responses based on the SNPs they test and existing research.