I don't think it's particularly reasonable for you to feel "used." When you volunteer information on the internet, anyone can read it. You don't necessarily know that the answer to the question is genuinely needed by the other person. I think of it such that I'm answering the question more to clarify my own perspective and perceptions of people than anything else, and I'm always grateful for that opportunity.
Personally, what I usually do on forums (except this one) is ask a question or two that I needed answered, wait for replies and follow-up with my reactions to them, perhaps answer a few other people's questions (if there are any that I know how to answer), and then leave. I would not feel "used" if someone merely posted asking for answers to questions, and didn't intend to provide anything in return. As far as I'm concerned, I'm just on a forum to answer other people's questions and look for answers to my own. I don't understand this sense of entitlement you think you have to "know" somebody and "expect" something from them.
That said, I didn't think Adam007 asked specific or significant enough questions for me to give a good answer. Also, I tend not to read the Relationship forum... I prefer discussions about introspection, ideas, feelings, etc.