I have a few items that I think would make skinning the forum a little easier.
1) threadcrumbs are currently within an H2 element and the topic title is with the crumbs. While it makes sense to have the topic title with the crumbs, it is not possible to style the topic title. Can the crumbs (including the topic title) be put into a DIV element and then another instance of the topic title put into an H2 so that it can be treated as an independent element? I think this would help with SEO because the only thing in the H2 would be the actual title of the post.
2) Icons - I really like the new icons you are using the forums on mojoPortal.com but I think if the icons were used as background images for the links they represent it would be easier for a site designer to specify their own icons for the links. The hardcoded IMG elements make it difficult to change the images on a per skin basis. This will also make it easier in the future to implement different icons for "new posts since your last visit" (which would be a handy little feature) because you would only need to apply a different CSS class to the post links that are "new".
3) Subscribe column doesn't have the headers attribute like the other columns. Can you add headers="subscribe" to the subscribe columns?
4) There are unnecessary <br /> after the postbody when viewing a post. The additional padding this provides can be done with CSS.
As always, thank you for such a great CMS.