Have you ever worked on your own website design? Do you design sites for your employer or for friends? There is a lot of work involved in creating the perfect site and while everyone will have different opinions as to what a perfect site is, there are a few UI gotchas that should be avoided universally. I stumbled across this wonderful screencast that points out some of the more irritating downfalls of website UI design.
And there is one thing I will add to that. Any site that you must log in to should make the log out link visible and near other account related links. I have a few bills that I pay where I log in and my menu with everything under the sun is in a bar on the left but the log out link is in 4pt font in the upper right corner of the page. BAD WEB DESIGNER! Go to the corner and think about what you have done.