I've been looking for a way to zoom in and out of PDF documents when they are previewed in Safari. And I found the way in the comments on this site...
Just control-click in Safari's window while previewing a PDF, and you will get access to a menu which includes zooming in and out, opening in Preview.app, and basic navigation. I suppose some people will find it obvious, but I think it deserves its own hint.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060317081739776