Hi,
When used with a YouTube video, it's not opening correctly the fancybox when using Safari.
The demo on this page is affected as well: http://plugins.josepardilla.com/fancybox-for-wordpress/demos/
To reproduce click on the link "This link shows some inline content in a FancyBox window" using Safari, first time nothing is loaded and the fancybox doesn't seem taking the correct dimensions, but if closed and re-opened it works.