If you've ever struggled to get an image to scale correctly in the PDF form of our documentation I "discovered" "scalefit" this afternoon.

Set it to "1" on your imagedata and it'll fit perfectly in HTML and PDF :)

<mediaobject>
  <imageobject>
    <imagedata fileref="whatever.png" format="PNG" scalefit="1" >
    </imagedata>
  </imageobject>
</mediaobject