AIM made a HUGE mistake by including invisibilty as a function. Clearly, it's intended purpose is to protect users from unwanted IM's. But, as in any experient, it's the unintended results that tend to have the biggest impact.

Obviously, everyone is going to want to be invisible. Who wouldn't? If you see a VIP, you can IM them without having to risk talking to someone you don't want to. Seems ideal. The only problem is that same VIP is thinking the same thing, and he/she is going to be doing the same. So, even if two people would want to talk to each other, they aren't going to be able to b/c they'll both be hiding from each other. Before you know it, everyone is going to be invisible and all the benefits of the IM universe will be destroyed. The beauty of IM is that it allows for selective/staggered/casual conversation. If everyone is online for extended periods of time, you can periodically im as need dictates. A funny link, a question, whatever. They are there, and you can contact them w/o it being a big event. With a phone call you basically have to be constantly going back adn forth for the length of the call. with im, communication is limited to a volunteer basis.

but not with invisibility. Now, people are going to be "on" (read: visisible) for less time. And so, when they are on, you are going to have to treat it like a phone conversation. Who knows when you are going to see so and so again, so you better get everything out of the way now.

Dealing with non-vip people is a small price to pay for the benefits of a fully visible IM universe. The away message is enough of a barrier to deal with such people / situations where you don't want to talk. If an away message isn't enough, then maybe you shouldn't be on IM at all.