I know that it is customary to point people in the direction of an FAQ, or to tell them to do a google search, when they ask a question that has been answered many times before. Many people get annoyed by answering the same question over and over, and I understand their frustration--however, I believe that we have a natural instinct to learn from another person. Not only do we have a desire for human interaction, but many people feel that answers from a person are more valuable than ones read in books. A good human teacher adapts the answers for the learner, where a book is unable to do so. There is also the benefit of hearing a personal account of experiences, especially when asking more than one person at a time, such as in a forum.
I like having sources at my fingertips that I can use to answer questions, such as pre-written paragraphs for frequently asked questions. I've found that directing someone to a website often makes them more confused as they sort through the information, while replying directly to them with the relevant excerpt (and a link) seems to help them more. If looking things up in books and on websites were the best way to learn, we wouldn't need teachers at all--we'd just need a reading list, right? But a teacher can pull out the key points, help weave them together, and make a subject easier to understand by filling in the gaps.
So, the next time someone asks you a question that you're sick of answering, remember that they don't know that you've been asked a million times; for them, it's their first experience with the subject. Come up with a document that you can draw answers from (an FAQ) and cut and paste a bit, then fill in the gaps when they ask more questions. I do my best not to get impatient, but I know that I do. I also get tired of having to rehash the same debates with people, but I've noticed that pointing them to a page that responds to each of their points doesn't work--they'll simply refuse to read it, so you have to feed it to them a bit at a time if you want your side to be understood.
It's hard to be patient, but it is worth it if you want to pass on your knowledge to someone else.