I also did not see a file called "AdobePDFViewer.plugin", but did see a file whose name contained "Adobe DLM" that I moved to trash. Upon moving to trash, it was called "AdobePDFViewer.plugin". I also went to Adobe Acrobat 7.0 Standard, internet and unchecked "Display in Browser Using". I checked back, and it didn't recheck itself.
Now, in situations where PDFs were set to automatically open, they don't. This allows the use of ctrl-click -> save linked file as, which makes my life a lot easier (can have several PDFs downloading in the background, can organize PDFs as I download them, can rename PDFs as I download them, doesn't cause spinning beach ball like opening PDFs in Safari).
I didn't do a check after each, so I don't know if either alone is sufficient.
Note that I had tried the terminal command suggestion earlier today, but it didn't work. I looked at the original MacOSXhints thread on this and someone posted that it didn't work after 10.4.2...
15 Powerbook G4 Mac OS X (10.4.3)