Tracing only if your trying to figure out a new style (can't tell you how often I'm trying to mix someone elses pretty eyes or hands into my drawings but never traced), but don't post it. For copying, I think it's the same thing with tracing, so I have no words there. As for eying, I think it should be okay. Cause you always put your style into it, and it helps inspire. As long as they don't claim it as theirs, and have permission, they should be able to post it up.