Sounds like you should consider selective style sheets for mobile devices. That way you can accommodate small displays and not at the expense of regular users.

While the white background helps, I tried to pay a bit of attention to type size and color contrast as well. The result of this effort is that you immediately know what's important, vs. what's not.

Two other things to consider:

1) Utility pane on the right, which I consider to be a big usability win (thread comments when you want them; your own comments when not on a thread)

2) A visual distinction for discussion threads vs. link threads