Somehow I always want to be pleasant with recruiters. Firstly because some of my friends are recruiters so I wouldn't treat someone in a way I would want my friends to be treated. Secondly because I kinda get "karma is a switch" feeling and don't want to be on the receiving end of that kind ("no, buzz off") of behaviour if I look for a job in a less then favourable state on the job market one day. I just like to personally reply, maybe even ask a few questions about the company, maybe there is an interesting idea or insight on it.