I have just tested the 1.5.4 gradebook and still found it has some usability issues. Here at SFSU we fixed some of these issues by adding borders to the gradebook, and for student's gradebook view, change it from listing everything horizontally to list everything vertically. For courses that has a lot (say, 15+ assignments and quizzes), this would really help with the display problem (people usually would want to scroll up and down rather than scrolling horizontally). You could download these our codes, screenshots and so on from:
Hope this helps, thanks!