@ johnny_D - If you get traffic from Google, then Google will watch how long the traffic stays on your site as part of deciding if they want to improve your ranking and send you more traffic. Also what the people they send do on your site, like visiting several pages. Of course they also notice if the person they sent to your site is immediately sent off to some other site. If they decide you're not trying to keep people on your site, they often decide there's little reason to send traffic to you.
Now, knowing that, you should be able to decide if doing certain things can hurt you.
HTH
