One thing that bothers me when I surf the internet: websites that have rollover advertisements and menus that pop up and cover what you’re looking at, particularly the ones that stay in their maximized form even when the mouse pointer is no longer over them. Navigating the web page to read it and/or follow links then becomes a matter of threading the mouse pointer between all of the active areas.
Don’t they ever do usability testing? Or don’t they care?