- Add some clue that the progress bar is in fact a progress bar (eg show "0% progress" by default) because I didn't recognize until I clicked an item.
- Move the progress bar below the "Usability Checklist" heading because the progress bar 'belongs' to the items below the heading. Again it's not immediately clear that the progress bar is a progress bar to me.
- Highlight the background of checklist items; the border is not obvious enough.
- Make the progress bar the same width as the copy container
- Make sure that the page is not too wide at large resolutions (I have 1600x900 and it's too wide for my liking). Always remember that people can only read an area of like one inch across at any time, so moving your eyes more than a couple of inches from the center can be taxing.
Again, those are my suggestions even they're written more like commands.