Viewers cannot communicate directly with each other. If you are connecting from different Viewers to two different Hosts there is nothing common between these two connections and they cannot affect each other.
Viewer for Mac, new mobile client for iOS/Android (with full fledged address book) as well as [possibly] Viewer for Linux will see the light at the same time since they are based on the same code framework. This is something we are already working on. I cannot give any ETA , unfortunately.
Don't hesitate to ask me if you have any questions.