As others have said, the fixed width of articles is a major issue. It's great that it doesn't expand to ridiculous sizes when the browser window is wide, but it's a problem for windows that are less than 1280 pixels wide too. Having a design that scales to narrower widths would also make it work better on iPads etc.
Also, Arial, really? There's much better choices available these days with webfonts. Arial is just ugly and hard to read, and neither it nor Helvetica were designed for use in body text.
I also have issues with the CMS, because there's a lot of inline styling that doesn't need to be there, but this is more of an under-the-hood thing that most people won't even notice. Stuff like:
<span style="font-size: 12pt;">
should not be there. Also, '12pt'? This isn't print, fonts shouldn't be sized in points on web pages. Use pixels, ems or percent sizes.