1. Almost 3 years
2. Animal suffering that is completely unnecessary in the western world. Also health and environmental benefits.
3. Sometimes; mostly when eating out or at another persons house, because I don't like to be rude or quiz people about what is in their food. Also, living with an omni who is addicted to junk food so there is always tempting convenience foods and candy, etc. around the house.
4. Yes. When most people find out you are a vegan, they react as though there is a implicit judgement of them within your belief. After all, you have made a choice for moral reasons, so this reminds them that not only is there a choice to be made, but that if they are not making the same choice their own morals may be in question. So I've been literally attacked by strangers who see what food I'm ordering in the cafeteria, or at the grocery store. It's pretty sad.
5. That you can't get enough protein, calcium, iron, etc., that your food must be bland and

ing, that all you eat is tofu, salad, or side dishes, and that you are uptight/bitchy/judgemental, etc. LOTS of stereotyping going on.
6. It's more like being a vegan is the result of who I am as a person, not the other way around.
7. Ask them to explain why they oppose it and then answer whatever questions are raised during their explanation. There really is no reason to oppose someone elses lifestyle choice, and the fact that there is so much bias against us is very telling in terms of our societie's collective dissonance surrounding the idea of eating animals.
8. We (and society in general) need to be more skeptical of claims that are made, both for and against veganism, so that we are not exagerating the benefits of veganism or the detriment of being an omnivore.