Usability - for Usable Websites
In times of Web 2.0 it is mostly "feelgood"-colors, clear-cut contrasts and a plastic look that can be seen on websites. This has its reason. A study published in Spiegel magazine shows that within just about 20 milliseconds, the human eye decides whether it wants to stay on a website. This is most important, of course, for "walk-in" users. Nevertheless, and that is the important part, you can transmit an emotion on the very first sight. This is why big beautiful pictures in the header section of a page are en vogue. Of course, if you don't get it right, you can make a lot of mistakes here.
Furthermore you can influence the behaviour of the visitor by sticking to the reading path (Kress / van Leeuwen): in western culture, we are used to read from left to right and from top to bottom. By placing content along this path you can prioritize them, thus controlling what a visitor will read first and what he will read after.
Elements which are too large will not be perceived. This, too, has been proved by a study: a download button which is too big is simply overlooked. This may seem paradox, but it's true. Generally you can say that a website is usable if the relevant information can be perceived by the eye right away and if the navigational structure grants access to all information by making a minimum of clicks using multiple paths.
Regardless of what this article may suggest, long texts on websites are useless. Text blocks longer than ten lines will not be read. You can tackle this problem by structuring your content, using boxes, lines, headlines etc. Furthermore, highlighted keywords will facilitate reading. Just one thing: please don't use italics. PC screens simply can't cope with that.
In general, when it comes to text, consider that just about everyone thinks he is a writer. That is not true. Good texts meet certain standards which more often than not are thrown overboard. While this is not the place to get into these standards at length, just a tip: it pays to pay someone for redacting or writing/ghostwriting. The message you want to transmit depends to a large part on the language you use.
Whether a company's website has an "About us" or a "References"-page depends on its activity. When I visit the website of a company which does webdesign, the first thing I want to know is about the projects the company has put through so far. Depending on the scale of the job I have to to offer I may want to know about the size of the company. Small firms, therefore, may refrain from presenting their team using fotos and self-portrayal. The references-page on this website is the one with the most hits...
All in all you can say that there is no need for more than five main navigation items. Momentarily, what you can see on most pages is the division into Company / Competences / References / Contact. This is totally sufficient. Everything else can be allocated somewhere in these sections. Too many navigation items tire the eye. Web 2.0 standards emphasize the 7-point-rule: never use more than seven navigation items, be it on root level or on any of the levels lying below.
Usability is a convergential matter
You will hardly ever find a website which unites all usability guidelines. Especially in cases where accessibility plays a role besides usability, the implementation of all standards can become a real challenge. You may thus say: the important thing is to be aware of these guidelines and to implement them wherever possible. Depending on the website and its content, these guidelines may be seen with a certain degree of relativity, and their implementation is always a commonsense matter including all context - always a convergence towards an ideal.