We currently use a google calendar to handle all of our studio wide events and tasks.
Wrap party dates.
Prospective Client Meetings
My solution for this was to create a project called "internal" and assign tasks to that but it's a little awkward and could be improved on by a global project of sorts.
When/If you add dependencies then producers could enter in scheduled vacation days and have those show up on any task the artist is assigned to automatically as a conflict.
Also with dependencies you could automatically black out or alert to conflicts between render farm scheduled down time and project deadlines. If the farm needs to go down for 2 hours but a project is due at 3pm and would fall behind schedule it would raise a conflict.
Even without dependencies this would be helpful.
One thing that is a big hinderance right now though is the lack of hour specific tasks. We sometimes have projects which have to be delivered at noon but milestones as days don't tell the whole story. It also puts a wrench in using milestones on a "internal projects" project as a scheduling tool.