Seeing that Acrobat is becoming more and more a hub of collaboration I think that it would be beneficial to have a chat capability as part of the basic functionality of the Acrobat family of products. Maybe the chat client is an AIR application that can tie into Reader and Acrobat to leverage their capabilites when necessary.  An example of this would be functionality enabled by Microsofts chat application which allows the exchangeof files though the chat interface.  For Acrobat users, I'm thinking that people would kick off collaboration sessions like shared review, or 1 to 1 connect sessions by first reaching out to their potential collaboration partner with an Acrobat chat message, then if the other person is ready to engage in collaboraion they could kick off the meeting or the shared review by clicking a button in the Acrobat chat UI.  Incorporating chat into the Acrobat family would also give users the ability to have one less application on their desktops, thereby simplifying their desktop image and potentally allowing large corporate customers to save money on software implementation, maintenance and support.  Also, seeing 90% of desktops have the Adobe Readerall Acrobat chat users would instantly be able to chat with almost any other internet connected Acrobat chat users