How do I set Safari on Mac OS X to show PDFs using Preview instead of Adobe Reader?
The "Right Way" to accomplish this is actually within the Adobe Reader app. Just go into preferences, click Internet, and uncheck Display PDF in Browser. Simple and non-destructive, since Adobe will almost certainly attempt to "repair" itself when it notices the plugin file missing at the next security update.
It is neither necessary nor sufficient to uninstall the Adobe Reader. I went also through this process and finally succeeded by (re)moving
/Library/Internet Plug-Ins/AdobePDFViewer.plugin.
More information can be found here.