That is strange, as in IE and FireFox, it is correct at my end.Try killing your cache, by going to tools--delete temp files. I know Pat is blind and has his set at 800x600 or something, but I can't make it do what you guys are seeing.
BTW, if you use "NEW POSTS" IN THE Nav Bar to jump to the new post since your last visit. Then on the left, you hit "View First Unread" and it takes you right where you left off.
I was able to duplicate the non-centering in IE, I didn't touch that coding so I have no idea.
For security as well as a nicer browser, I recommend using FireFox, its free, you might try it. You can have both, actually, I also have Safari