This is Byzantine beyond belief.
1 On iBooks I did something that was like "Transfer books to from iTunes" I thought I was screwed at that point but maybe not.
2 In iBooks I selected PDF on the bar on the left. I was presented with a window of thumbnails of the PDFs
3 I tried to 'drag and drop' one of the images to a normal directory that was open in a Finder window.
4 Shazam, off it went.
/Byzantine-start
5 Switched to 'list' view.
6 Selected 11 files.
7 Mouse absolutely refused to drag-n-drop
8 Switched back to 'Thumbnail' view
9 Highlighting a number of files and then dragging and dropping worked fine.
/Byzantine-stop
So it can be done and I am sure that this is very intuitive to some people. I hope this helps those who need this feature.