Apple’s patch notes:
Plug-Ins & Zooming
Please test interaction with plug-ins and the appearance of plug-in content while zooming. Please test zooming using gestures and keyboard shortcuts.
Please test printing PDFs loaded into Safari as well as PDFs displayed in iframes. Using PDFs Printed from Webpages
Please test links in PDFs created from webpages using Safari 5.1.4.
The developer seed requires Mac OS X 10.7.3, which was just released to the public on Wednesday. Safari 5.1.3 was released at the same time.