Today I made the mistake of downloading and installing Adobe Reader 11 on my Mac running Mountain Lion. I thought it might solve some issues I was having opening bank statement downloads. (It didn't.)
Adobe Reader is nice enough to ask if you want it to be your default application for .pdf files.
However, it does by default install itself as your new best friend in Safari. Where I was used to clicking a PDF link in Safari and getting a window with minimal embedded Preview.app controls, I now got all of Adobe's madness, with non-standard download and print controls.
There was no place in Safari or Adobe Reader preferences to turn this off. To make it go away I used the following
$ sudo rm /Library/Internet\ Plug-Ins/Adobe*
This removed the files
AdobePDFViewerNPAPI.plugin, which seems to have me back to normal.