Honestly, there's so many claims and so much BS out there that started with Pauling that I really can't make any definitive statement other than, "yeah, we need it." But how much is good? I don't know. From my trusty Merck Manual (home edition,) the synopsis is this:
"Vitamin C Deficiency: Vitamin C is essential for the formation of connective tissue. It helps the body absorb iron and recover from burns and wounds. Pregnancy, breastfeeding, overactivity of the thyroid gland, various kinds of inflammation, surgery and burns all can significantly increase the body's requirements for vitamin C and the risk of a deficiency." Then they go on to list scurvy, bleeding gums, weakness, fluctuations of BP and heart rate.
"Vitamin C Excess: 500 to 10,000 mg have been recommended by some to prevent the common cold, schizophrenia, cancer, hypercholesterolemia and artheriosclerosis. However, these recommendations have little to no scientific support. Doses higher than 1,000mg/day cause diarrhea, kidney stones and changes in the menstrual cycle. Some people who stop taking high doses develop rebound scurvy."
Their listed Daily Adult Requirement is 60mg. So, my opinion is that you adjust that number within reason, for any particular condition you might have. But, if you drink fortified juice and eat the right foods, there's probably no real reason for supplementation.
Ever take a vitamin and notice how it changes the color of your urine? Yep, that's all the water soluble vitamins that you just paid a fortune for being flushed down the toilet.