Safari 3 Beta kept crashing on PDF links for me. I found and removed an old Adobe PDF viewer plug-in, and all is well again. Use the Finder's search feature to locate AdobePDFViewer.plugin (it should probably be found in /Library/Internet Plug-Ins/), and delete it. Restart Safari 3, and the crashes may be gone.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070622185034973