These very closely apply to Web/Internet/Application development's downfalls. Not including the user in the development phases and/or testing with users early and throughout the development process. Having a development team that does not have a balance of visual, technical, and production skills can be problematic. Lastly, projects that are technology for technology's sake, very rarely offer success.
Conversely, success comes from getting these things right, involving the user and understanding how users would interact and use what you are building. Having a balanced team so that visual, technical, and production issues can be addressed and solved appropriately. And lastly knowing when and how to best use what technologies will drive success.
This last element, understanding the technologies, will help you get over the hurdle of accessibility/508 compliance. It will also help you find the best tools to interact with the users of the site/application. Having DHTML elements to provide action on a site or to serve information, when the user audience does not fully have the capability of addressing or handling the presentation, will have detrimental effects. Know what your elements your users have turned on and off in their browsers and what versions they are using. It is important to know what threshold of user profile can be the cut-off for developing a site. If 10% of your users have JavaScript turned off should you still develop elements of your site that are JavaScript dependant without providing an alternate service? Know and set this percentage threshold, as it will help understand why you can and can not use certain technologies.