There's new data about calcium, fractures, and vegan diets. This study showed that vegans overall are 30% more likely to have a bone fracture than lacto-ovo vegetarians, fish-eaters, or meat-eaters:
Appleby P et al. Comparative fracture risk in vegetarians and nonvegetarians in EPIC-Oxford. Eur J Clin Nutr, Feb 7, 2007.
Jack Norris of Vegan Outreach has an excellent discussion of the results.
However, those vegans who consumed over 525 mg/day of calcium had the same risk of fracture as the other populations in the study.
When calcium is consumed with large amounts of protein, such as in milk, calcium excretion in the urine increases. Therefore, it has been suggested that vegans have lower dietary calcium requirements.
I think that this study suggests that perhaps we do need to be more diligent with our calcium consumption. Most people need 1000 mg/day of calcium; pregnant women, the elderly, and children may have higher requirements.
Also, be mindful of getting enough Vitamin D, which regulates calcium absorption. Fifteen minutes of sunlight a day will give you enough. But, if you are in a northern climate or do not get that much sunlight, make sure you are consuming either a multivitamin with Vitamin D or Vitamin-D fortified soy or rice milk.