It's never reset my level, perks, or skills, but a couple of times it did redistribute my magicka/health/stamina to be equal, instead of the distribution I had chosen when I leveled up. That's also easily fixed with the console, though.
But, like I said, I never used showracemenu to change race, only to change other things about my character's appearance. I've read that what things get reset can vary based on what things you change, and that sometimes you can even get your hands re-bound by using showracemenu, so... save first?
