You can grab the selected item anywhere to drag it to a new position. I have added your suggestion to make this more obvious to the list of enhancement requests though.
Yes, I did figure out the grab and move, but I couldn't JUST grab it. I have to first click on the line, then click and hold to be able to grab and move it.
If you right-click in a SQL window and 'Add to Project' you get a blank line in the list of items. I find this useful for seperating items into related groups.
It would be good if you were prompted to save any changes in the Project window when you quit PL/SQL Dev and have forgotten to click the Save Project button!!