Jason Doucette rightly points out that nutrition-dispensing folks tend to give finger-wagging advice to vegans when the exact same advice typically holds true for omnivores. Bitterly funny analysis and well worth reading.
That said, vegans—like omnivores—definitely ought to read up on nutrition. And Jack Norris’ VeganHealth.org site is probably the best place to get genuinely useful vegan-specific nutrition information. (Thanks Nancy.) Link.