I believe that if you make regular choices to eat a variety of foods and maintain an overall healthy lifestyle that, in general, dietary supplements are an unneccessary waste of money. That being said, I don't see why taking a pre-natal vitamin while not pregnant could be harmful. Possibly unpleasant from side effects like constipation etc. but that could happen with many of the brands of vitamins available on the market.
It will be interesting to see what everyone else thinks :)