I always responded to anyone that expressed an interest. I just think its an nice thing to do. Even if you say that you are taking a break or that you've met someone and you'd like to see where it goes. I also do not think that its inappropriate to say that you just don't feel a connection and with them good luck. I would never be rude. Dating is tough enough and on-line dating even more so and I don't want to make it worse. I always appreciated a response so that I knew what to do - close out, wait, etc... Hope this helps and good luck!