As consequence of the blog layout discussion, I added a background color to comments, clearly separating them. Tell me if that works better for you.
On the issue of some people preferring the text to not use the whole width of the screen, I can only recommend making your browser window less wide if the text is too wide for you. Unfortunately Google Analytics tells me that my blog is read by people using anything from 320 pixel to over 2000 pixel wide screens, and telling the blog to use "all of it" is the only viable option.
[EDIT: Color changed to that of the sidebar, and added a border and padding. I also added a max-width of 1280 pixels, based on usual screen resolutions of people viewing my blog as reported by Google Analytics. Unfortunately that max-width works on my computer only when I use Firefox or Chrome, not with IE7. The preview works with IE7, but once I save it, Internet Explorer just ignores the maximum on my computer.]