Bad Search

A related problem is when search engines prioritize results purely on the basis of how many query terms they contain, rather than on each document's importance. Much better if your search engine calls out "best bets" at the top of the list -- especially for important queries, such as the names of your products.

PDF Files for Online Reading

Users hate coming across a PDF file while browsing, because it breaks their flow. Even simple things like printing or saving documents are difficult because standard browser commands don't work. Layouts are often optimized for a sheet of paper, which rarely matches the size of the user's browser window. Bye-bye smooth scrolling. Hello tiny fonts.

Scrolling Text, Marquees, and Constantly Running Animations

Never include page elements that move incessantly. Moving images have an overpowering effect on the human peripheral vision. A web page should not emulate Times Square in New York City in its constant attack on the human senses: give your user some peace and quiet to actually read the text!

Of course, is simply evil. Enough said.

Long Scrolling Pages

All critical content and navigation options should be on the top part of the page. Users will only scroll if they believe that there is something useful lower down the page.

Non-Standard Link Colors

By default links to pages that have not been seen by the user are blue; links to previously seen pages are purple or red. Don't mess with these colors since the ability to understand what links have been followed is one of the few navigational aides that is standard in most web browsers. Consistency is key to teaching users what the link colors mean.

Fixed Font Size

SS style sheets unfortunately give websites the power to disable a Web browser's "change font size" button and specify a fixed font size. About 95% of the time, this fixed size is tiny, reducing readability significantly for most people over the age of 40.

Respect the user's preferences and let them resize text as needed. Also, specify font sizes in relative terms -- not as an absolute number of pixels.

Opening New Browser Windows

Designers open new browser windows on the theory that it keeps users on their site. But even disregarding the user-hostile message implied in taking over the user's machine, the strategy is self-defeating since it disables the Back button which is the normal way users return to previous sites. Users often don't notice that a new window has opened, especially if they are using a small monitor where the windows are maximized to fill up the screen. So a user who tries to return to the origin will be confused by a grayed out Back button.

Overly Long Download Times

I am placing this issue last because most people already know about it; not because it is the least important. Traditional human factors guidelines indicate 10 seconds as the maximum response time before users lose interest. On the web, users have been trained to endure so much suffering that it may be acceptable to increase this limit to 15 seconds for a few pages.

Even websites with high-end users need to consider download times: we have found that many of our customers access Sun's website from home computers in the evening because they are too busy to surf the web during working hours. Bandwidth is getting worse, not better, as the Internet adds users faster than the infrastructure can keep up.

Flashturbation

When used well Flash gives you the freedom to create an unrivaled user experience but (and this is a pretty BIG but) it is dangerously easy to get carried away. Splash pages and animated banners don’t achieve anything other than distract from your content. Use Flash only when it serves a purpose which directly benefits the audience or don’t use it at all.

Site doesn’t work on a mac

I’m a Mac user so I freely admit that I’m biased, but it really frustrates me when I can’t use a web site with my Mac. Thankfully this is becoming less common as more people get seduced by slick apple marketing campaigns, but it still happens occasionally and it still bugs the hell out of me. Web designers can pick up a cheap 2nd hand imac off ebay for buttons and use it to test sites. Plus itunes makes it a great office jukebox!