clipped from: www.useit.com Summary:
Users often see online content out of context and read it with different goals than you envisioned. While you can't predict all such goals, you can plan for multiple uses of your text.
No matter your medium, it's fairly standard advice to simply write for your readers and their tasks. For old media, reader goals are well known, ranging from being entertained (when reading a mystery novel) to getting investment ideas (when reading the Wall St. Journal's "Markets" section).
Writing for the Web differs, however, because various users might approach a given piece of content in different ways: