For anyone confused by the OP, the instructions are for Mac OS X only.
For Windows Vista/7/8:
C:\Users\[Your Username]\AppData\Local\Plex Media Server
For Ubuntu 10.04 (older/newer YMMV but it shouldn't be too different, if at all):
/var/lib/plexmediaserver/Library/Application Support/Plex Media Server/
You'll have to create a new folder named "Scanners" and then sub-folders in there for each scanner type you want to use (Movies, Series, Music).
I installed BABS and the path looks this: C:\Users\Justin\AppData\Local\Plex Media Server\Scanners\Series
To get to the AppData folder you'll either need to enable viewing hidden files and folders via Folder Options or type the path directly in the Windows Explorer/My Computer address bar. Another way to get there would be to right-click the Plex icon in your taskbar and go to the Plug-Ins folder then go up a folder.
Side note: the Plug-ins folder in C:\Users\[Your Username]\AppData\Local\Plex Media Server is where you want to install any plug-ins you want to use.
