We updated the version of jQuery used by our CMS recently (1.3 -> 1.4) and noticed a stylesheet written to the page header after it loaded was being ignored by IE7/8.

Turns out that if we wrote the <link/> tag to the header first, then wrote its attributes, everything started working again.

Worked in jQuery v1.3:
jQuery('<link rel="stylesheet" type="text/css" href="myStyles.css" />').appendTo('head');
Works in jQuery v1.4:
var cssLink = jQuery('<link />').appendTo(jQuery('head'));
  rel: 'stylesheet',
  href: 'myStyles.css'