I would love it if there was a feature in which tasks could be assigned how long they would take in hours, and could be assigned what hours in the day the task is worked on. For example a task that would take 2 hours and would show up on your daily calendar for those specifically assigned hours as blocked of, so that no one could assign a project that would overlap. Similar to iCal or Google Calendar.
This would be most helpful to make sure no one is overworked. So often where I work, project managers will just assign tasks, with no regard to how many I have on that day or how long one task would even take. For example, it might take me 5 minutes to complete one task, when in another situation it might take me 6 hours.
I hope this makes sense and you can see the vision behind this idea.
Ryan Monette commented
And another thought, it doesn't necessarily have to be assigned a specific start or end time on the day, but could just be blobs of hours increments in the day to help project managers at a glance see how full someones day is.