It's visually desirable to keep the line connecting an event to its date vertical - would it be possible to have an option that would constrain the dragging to vertical shifts only?
Robin Dawes commented
Holding down 'shift' to force the vertical alignment is a great idea.
This would be really useful. What do you think of holding down the 'shift' key as the control for locking the event vertically? this would make it very similar to a lot of popular applications (e.g. PowerPoint and Photoshop).