I came to StackOverflow with a question I knew would be difficult and specialized. As soon as I found out about the bounty system I went to work collecting reputation so that at 48 hours my reputation would be over 300 and I could offer that as a bounty, if my question did not already have an acceptable answer. I have always tried to be a net contributor to any forum I use to get answers to my questions, but I was definitely working to gain reputation during the 48 hours from posting my question to it becoming eligible for a bounty.
I did not see anything obviously unethical about, in effect, trading my time and existing skills for attention to my question in an area I'm learning.
However, I've since seen references to being a "reputation-whore". Was deliberate reputation-hunting with the intent of being in a position to offer a bounty against local standards?