These observations are based on ten years of usability testing at Kayak.com, including eye tracking sessions where we studied what part of UI was actually scanned by users.
Most web pages have too much clutter. Programmers think their ideas are important, and they always want to add more and more stuff to each page. However, that results in pages which feel confusing and slow, and businesses that need lots of marketing vs. repeat traffic and word of mouth.
Sometimes programmers add little tips on their web pages. However, if you need tips, your user interface is not simple enough.
I think that when most users encounter a new web page, they look only for these elements, in this order:
So if you want to create a succesful web application, get all the noise out of the way.
See also code.