As you go to add a new event on your calendar, if you already have an event scheduled on that day in ANY calendar, you will be see Schedule to the right appear in Yellow:
You may of course still add an event (double booking) but this is just a friendly little reminder that there is in fact a conflict. If the conflicting event has an associated project, you may also click on it to be redirected to the specific project page.
You will also notice that when adding project dates for events that have conflicting times on your calendar, they will now appear in red:
Keyword Search: Calendar, Conflict, Dates