Well, it's probably not much help since I'm on a 22" monitor, but here it is in widescreen. Of course it leaves a lot of empty space on the right side of my screen, but that's pretty common for me with webcomics. They either align to the left, or in the center leaving the sides empty.
I shrank the Firefox window to try and get an idea of what you meant about the twitter box, and I wouldn't say it looks bad at the bottom of the screen, other than it kicks the navigation buttons down. There should be a way to set it so there's a horizontal scroll bar instead of rearranging the page on smaller screens.
I could have sworn I used to have a site bookmarked that tested websites for this specific thing, but I can't find it in my old bookmarks anywhere. Basically you type in a site address and it takes screen shots of it to show how it looks on a variety of systems, monitors and browsers. I'll try to remember it.