The sidebar is a bit of a kludge right now and will probably be modified later anyway. In IE6 it behaves like a normal sidebar, but in IE7 or Firefox it's fixed and doesn't scroll along with the text. I personally don't like the fixed position aspect, but it was the only mod I found that worked on all pages rather than just the forum home. I'll need to dig into the templates to find a way to make the behavior uniform, so it works like a normal sidebar. It's not as simple as cutting a few lines from the CSS.
Over time many visitors to the forums will enter via search engines or other links rather from the main site, so I thought it important to have some high visibility links to other parts of the site. I also find the default forum width too wide and prefer to read in thinner columns.
I'm not certain what I'll do with the sidebar in the long run yet. I may use it to highlight popular threads/posts or other things like that.