On my vbulletin big board one of the most popular functions is to see which users are in the same thread and what they are doing. This is mighty useful when you are about to write a reply, but you see that someone of interest is also writing a reply. Its also great for the community feel and the sense of interactivity. Its a usergroup permission and one of the reasons why my members purchase a VIP member subscription. It would be very nice to have this function available for XenForo. Such functionality needs to be well coded, as the frequent polling of the server can easily cause problems if its not well done. Especially for active communities.