Here's a modified CSS for large fonts. It's not done yet and I'm also waiting for Tom to get back to me about whether or not the markup can be changed on a per-theme basis. When i have some time I'll play in the admin interface to tune this all up.

I've removed the double outline around posts as well as the black space between them. Also change is the subject heading for each post, though because of markup I'm unable to make it the same as it used to be (need to move where a table cell gets created). But I did push the subject over so it better matches where it used to start in the old forum (same indentation as the message body instead of being pulled over the poster info/icon)

I've used ems for everything except the quotes. Because ems are always based on the parent's size, nesting quotes would progressively make the text smaller. Specifying as pixels for this was the work-around.