User blog comment:Susanolivia/Fixed Width, Sidebar, and the Removal of Monaco/@comment-785068-20101004184613

''Implementing fixed width solved the wiki page design problem, but that left the issue of collision with the 300x250 box ad. In order to attract advertisers to our site, we need to have a 300x250 ad near the top of the page -- this is a standard ad unit that we can’t do without. Until now, we’ve floated that ad inside the content space -- a compromise that nobody was happy with. That ad interrupts the flow of the content, and it causes unexpected collisions. We needed to solve that problem, too. We investigated a lot of different options -- and in the end, we found that the best choice was to set the sidebar width to 300 pixels.''

Thank you for answering the question about fixed content space. I'm not sure if it's entirely wise to decide this factor on pixels, but thank you all the same.