Am I suffering "divitis"? (CSS especialist needed)

It looks perfect. This should be taken as an example!

One symptom of "divitis" is when you see a list of <div>'s instead of using a <ul>.

You're using <ul>s for navigation, and <h1><h2> for headings - that's good enough for me. I couldn't think of a more fitting element for any of the divs you are using. Would pass my quality check without further ado.

For the most part your markup is fine. Each site presents slightly different problems. I would argue that your code could be improved by removing #intro and just applying the CSS to the two columns.

Depending on the rest of your page, you may be able to do without the #header div.

Additionally, you can style html AND body if needed to help with multiple backgrounds/containers. Just remember that body starts acting like a div (doesn't extend to the bottom of the browser) as soon as you start applying styles to html.

Using divs or the new HTML 5 block elements, is all about making semantic sense first, and giving places to hang your CSS second.

Since each of your div elements serves a specific purpose where they provide semantic grouping of elements that go together, I would say your code is just fine.

For the record, this is divitis:

<div class='image'>
  <div class='shadow'>
    <div class='bottom-shadow'>
       <img src="..." alt="" />
    </div>
  </div>
  <div class="clear"></div>
</div>