i used to append stylesheets with query 1.4.2. Example:

if (!$('head link[href*="jquery.fancybox"]').length) $("head").append('<link rel="stylesheet" type="text/css" href="../_content/layout/default/_shared/js/fancybox/jquery.fancybox-1.3.1.css" />');

... without problems. After updating query to 1.7.2 that doesn't work with ie8 anymore. I know, that I could help myself with  document.createStyleSheet(), but that means more code because it isn't a crossbrowser-solution and I ask myself why the code above works without problems in jq1.4.2 but not in jq1.7.2. 

best,

heinetz