Text Content Inside Images
You should never use images for your content text. It's inaccessible, hard to read, and can't be resized or found by search engines. In fact, I recommend never using text inside images. The only exception would be if you're using a CSS image replacement technique.
Blinking, Scrolling, or Animated Content
Text that moves is even harder to read than text in images. And blinking elements on a page can be very distracting. In some cases they can even cause seizures or other medical issues. Anything that could cause someone to get sick should be avoided in your design.
Using Ajax for Content
It can be fun to create Web applications using Ajax, but if you hide content inside an Ajax device, you may cause more problems than you solve. You should use Ajax for elements that change on your website. Content generally doesn't change, so it shouldn't be in an Ajax device.
Resizing the Browser Window
It's one thing to open a popup window and resize it. It's something completely different to resize the current window that your reader is in. Chances are they have it open to a size they are comfortable with. It may fit their monitor or the other pages they load. When you resize the window, it is annoying and intrusive. And it makes people uncomfortable. And an uncomfortable customer is a customer who is gone.
Loading Your Website in a Popup Window
Another common trick is to use a popup window to load the entire site. Some people do this to hide their page locations or in some other misguided attempt to protect their content. The reality is that this won't protect your content, but it will annoy your customers so that they won't return. Forcing your readers to view your page in a browser designed by you, which is essentially what loading it in a popup window is, is just as intrusive as resizing the window.
Components That Don't Work
Last week I went to a Web page that provided an inbox for an online mail client. It would show 15 mail messages at a time and how many messages you had in your inbox. Next to that number was a button that read "See All Messages". However when I clicked on it, it would only show the next 15 messages in my box. Since I wanted to see all my messages so that I could delete them all, it was very frustrating that I could only see 15 at a time. It would have been less frustrating if the button component hadn't said "See All Messages", but because it did, I clicked on it several times before I realized that it was simply broken. I deleted my account from that site, so that I wouldn't have to deal with their horrible inbox any longer.
