I actually view Chrome's PDF plugin as a complete abomination (at least on the Mac), and go out of my way to nuke it. It's slow, and there is _no_ easy way to open the PDF displayed in a PDF handling app (i.e. Preview) without resorting to copy and pasting the URL into wget.
Cmd + S or using Safari
You can open PDFs displayed in Safari in Preview without saving them to the disk. (There is also a button that puts the document in the Downloads folder.) Chrome’s PDF viewer is better than Adobe’s plugin but worse than Safari’s PDF viewer.