I was moving content from one WordPress installation to another one and encountered a problem.
I had Youtube-movies embedded via iframe. These posts are exported correctly, at leaset the iframe exists in the .xml file.
<content:encoded><![CDATA[<iframe src="http://www.youtube-nocookie.com/embed/HddnfmOzmcg?hd=1" frameborder="0" width="560" height="315"></iframe>]]></content:encoded>
After importing the .xml file the iframe was gone. Not sure if this is a problem with the importer or the exporter, but I encountered this problem on two occasions with different installations (all were WordPress 3.2 though).