There's no need to even turn on an instant messanging system if you won't be around to answer it. That's my philosophy. If I don't want to chat on AIM, I don't turn it on. Being "available" means just that. You're telling people that you're around to chat. Not answering IM's is telling people that you're around to chat, but just not to them. If you set an "away" message, then that changes everything. I only have problems with people who are "available" which tells me that they're at the comp ready to chat, that don't respond.