I like the application of google which is part of google docs - "Google Presentations".
I tried it several times. It seems that combine all the features with IM tool is giving it great benefit. I spoked yesterday with another person who watched the same presentation as me at the same time. Not suprisingly, we found a lot of common and shared a lot of knowledge.The starting point for ours discussion was the subjects regarding the presentation- web 2.0. For doctors it can give added value to find other professionals in their field and talk with them live. So simple but so friendly and useable. As i mentioned, the subject was web 2.0. Here is the link for the presentation ( you need to have Googles account). One interesting idea behind the presentation is "collaboration concept". You can write to the author and suggest new ideas for the content. You can become collaborator of this presentation. Its sounds like the concept of the Wikis but from the "presentations side". So the concept is truely nice and interesting and the content itself is the same.