I just came across this example of a longstanding usability beef of mine: menus consisting of tiny unlabeled buttons.

Why is it annoying? Try browsing through the images in the illustration section. As the buttons have no labels (or rollover descriptions), there is no reason to click one button over another. This leaves 2 choices: click on the buttons in sequence or at random. Clicking in sequence is difficult because each time you want to go to the next image, you have to move your mouse precisely 5 pixels horizontally with no vertical movement. This causes you to focus on your cursor, when you should be focusing on the images. Clicking randomly has an extra problem, in that you cannot tell what images you have already viewed, so you are likely to view the same image multiple times.

This example is noticeable because otherwise the site is great: fantastic illustration and nice audio.

There are various solutions to this problem. The simplest would be to allow the user to skip to the next image by clicking on the current image (or add a next button).