Category Notification is even better than what i tried to do, thanks for that. I know there is the Chat function but i was imagining something like a "Reply with PM" function in the Reply dropdown, guess that does not exist or is there a plugin for that as well?
Live threads in sidebar
Is it possible somehow to have a sidebar widget that displays the live threads for the category the user is in when viewing a post in that category? So for example you are viewing this thread in the technical support category, in the sidebar now you'd see the latest threads (not individual posts) in technical support. If a new thread is posted as you're reading this, that widget would update with that thread at the top...