According to this article there are five things users hate the most from websites:
1. Invasive advertising
2. Re-inventing the wheel: having to learn how to use the website i.e. bad UI
3. 'Leap of faith' links: disclosing information on content and file size
4. Attention-deficit Web sites: flashing icons and banners
5. War and Peace length: Users read 25 percent slower on the screen than on paper so long texts and scrolling down is annoying to them
