Some really interesting points above. I've been vegan since 1984, which (in the UK, at least) means that for a lot of that time, most people I met casually didn't even know what veganism was.
I became vegan for ethical reasons - I worked for a time as a dairy herdsman, and didn't like what was going on in the industry. I never took any supplements, other than B12, and relied on the vague (and probably daft!) idea that if I mixed proteins and ate a good range of foods, then I would be OK. In fact, it has worked out fine so far. Fifty seven years old, everyone says I look a lot younger, three children, a demanding job, and (before the joints complained!) third Dan in a martial art. I have recently started taking a little ground flax seed because of all the publicity around it, but up until a couple of years ago I had never heard of it. I might of course have been very lucky health-wise, but I might also be a fit and healthy reason for vegans to drop some of their excessive worries. If I don't post for a while, someone might want to PM me to see if I have dropped dead due to my dietary deficits catching up with me!
Manas' points are very interesting. I am extremely aware of the smell of milk and egg products in food. For me, they are slightly repellent and just don't smell like food any more. The only time I knowingly deviated from the veganism was after a Vipassana retreat when there was a celebration and some Indian people cooked a big dish of sweet milky rice. Not wanting to disappoint them, and all too aware that "veganism" is just another identity to cling to, I indulged. Two hours later, I was wondering who had spilt the sour yoghurt on my clothes - a really cheesy and nasty smell which I couldn't shake off. I realised that I was actually sweating it out. It seems that I have lost the ability to digest milk etc., and now might lack the enzymes or whatever deals with it once ingested.
Anyway, that's just my story. Good luck with yours, and may whatever you eat bring you good health and happiness.