At the moment, the markup of box titles is <div class="title">A title example</div> while it should be either <h1 class="title">A title example</h1> or <h2 class="title">A title example</h2>.
Whether to use h1 or h2 is hard to agree on :
Using h2 for box titles would leave only one h1, the one of the document in the HTML page, which is semantically good. In the other hand, h2 box titles would promote boxes as sub-elements of the main document, while they really feature separate documents.
Using h1 for box titles with the first h1 to appear in the page rendering being the h1 of the document title is the best semantical and structural solution. But this implies to not have boxes in the current left column.
So a first implementation could be to use h2 markup. People wanting to use h1 markup could patch the SimpleBox?.py and skins/CPSSkins/cpsskins_portalboxshape.dtml files.