Some users have issues displaying PDFs in their web browsers. In some cases, when clicking on a link to a PDF, they get a blank black or white page. These issues can be caused by certain PDF browser plug-ins.
Michael Cohen has written an article for TidBITS discussing this issue, and explaining which plug-ins to remove.
I haven't seen this issue myself, but for those having problems, this is a simple fix. It's worth noting that, over time, you may have browser plug-ins that you don't need, so it's worth having a look in ~/Library/Internet Plug-Ins and /Library/Internet Plug-Ins to see what's there.
Mac OS X Hints