"The difference between a great design and a lousy one is in the meshing of the thousand details that either fit or don't..." - Ted Nelson
Great online services result from careful attention to the details. Of course, it's necessary to understand the details before you can attend to them.
Here are some common mistakes to avoid in developing web services.
Who are you... where am I?
Web sites can give users a very real sense of disorientation. For example, it's common for even commercial web sites to fail to identify the organization behind them (we dare you to visit the TAPPI web site and figure out what "TAPPI" stands for). Just as bad, many sites offer no indication of their purpose or mission, or the organization's physical location.
Information?
It's fairly common to see the word "Information" used to describe a section of a web site. We are still waiting for someone to explain to us which part of a web site doesn't constitute "information."
Plug-in purgatory
Pity the proprietors of web sites that require the use of plug-ins (additional software programs that work in concert with the web browser). This reflects the arrogant thinking that site developers can control the user experience, as opposed to working hard to optimize it. With rare exception, it's a sign of bad judgment. Web users have good reasons to avoid unknown software applications and will likely decline to change their computer configuration for the sake a single web site.
Hijacking the experience
Along the same line, many web sites use other techniques in an attempt to control the user experience. These mistakes include splash pages, locking the browser window size, disabling the back button and using pop-under advertisements. All of these tend to alienate users, who are smart enough to know that they ultimately control their web experience, and can go elsewhere to get it.
Click here, click there
A good sign of a clueless web writer is the use of the words "click here" as a web link. Text links should always be incorporated into the flow of the text, rather than interfering with it.