We use this system for Product Development and Maintenance.
Some of our maintenance reoccurs weekly and monthly, would love a Repeating task option. Where you can just set the task to create a new one configured completely on the old one (including Estimated time, etc), based on schedule (weekly, monthly, day of week, day of month, every third Friday, etc).
On the old forum, AviD got 73 votes for this:
Repeating or Permanent Tasks.
For instance, there are often tasks that need to be performed every month, or week. Currently the choice is either repeatedly duplicate the same task, and each time set appropriate date, or just leave it open as a schedule item. This can be a "special" kind of task, or maybe expand the schedule item type. Also, this might be used for a "Release Checklist".