This probably affects anyone that has tried to make a fixed width master page in SharePoint 2010 (unless you have already noticed the error) it affects the MSDN article Upgrading an Existing Master Page to the SharePoint Foundation Master Page and my Starter Master Pages (expect an update to my starter master pages very soon).
In the article it states:
If your page is fixed width, add the class s4-nosetwidth to the bodyContainer div element. The updated div element would look like the following.
In actuality you need to place the s4-nosetwidth on the previous div tag like this:
Without that line SharePoint injects CSS inline to your
and sets the width the current size of the browser (which completely wrecks most fixed width design).