Web site designers should think hard about how to keep users from muddling around on their sites. "Users muddle when it isn’t clear what they are supposed to do in any given situation." http://www.alttags.org/archives/2004/06/29/37/
Home for Jeff Johnson's book "GUI Bloopers". Covers problems with text, graphics, interactive dialog and web design. Table of contents available for viewing, and Chapter 4 ("textual bloopers") available for download. http://web-bloopers.com/gui-bloopers/