Gantt Chart Bracket
 

Can someone explain why I have a "[" bracket and subsequent gray lines on the far right of my Gantt chart task bars? All of a sudden they started to appear on any new task created. What button did I inadvertently press? What do these brackets mean? How do I turn them off? Thanks.

You added all of those tasks after the project started, right? They indicate the presence of a start constraint (at the point of the '[') and the bar indicates that OmniPlan scheduled them later than the constraint.

In OmniPlan 1, those tasks would be jammed up at the left end of the Gantt chart unless you'd explicitly done something to make them be scheduled later. In OmniPlan 2, it was decided that most people don't add tasks to their plans in the past, so any tasks added should have a start constraint that makes OmniPlan schedule them no earlier than the day they were added.

If you want to get rid of those constraints, you could select the bunch of tasks, bring up the inspector, and clear the start constraint date. However, if you don't do something else, like assign some resources and dependencies, they'll likely end up back at the start of your project. They aren't an indication of a flaw in your plan.