I forgot to mention. You can generate a PREVIEW document using Briss. That was a nice feature. This would also be a nice feature if it were added to A-PDF Page Crop - although it is less essential because of the difference in the way the program views/shows you the pdf in the main screen. As I mentioned - a nice little feature of Briss is the batch analysis it does for you of all the pages - so that were the scan isn't necessarily uniform - it is easy to set different margins for the different sets quickly and easily. With A-PDF you instead get effectively the view of Acrobat - a main viewing/reading area (where you see the particular page you are on - and can scroll through the entire document) and a sidebar with thumbnails. That too is a nice feature. So you can effectively see what the PDF is going to look like before you process it - unlike in Briss. I still think - for "double checking" purposes - it would make an nice addition to A-PDF.
Also let me share with you what I found useful going back and starting to use the latter for more intricate editing choices before generating the new file (like bleed and trim). A very nice feature of the Acrobat-like interface is that it has on the menu bar a set of alignment tools as well as the alignment coordinates. So you can be EXACT in creating the two crops (each page) if you want/need.
There is also a feature in generating the output that you can set - to either use the dimensions of the crop rectangles - or to set the page dimensions manually (and it then would center your crop rectangle within that). This too will be nice when I start going back and editing some of my old scans. Particularly of the very ancient books - where I couldn't lay the book perfectly flat face-down on the flatbed scanner.
I hope this helps people. I have come across this topic posted in the forums here at MobileRead numerous times. I hope that I have been able to provide a good resource for others looking for this information in the future. [I am actually excited - it is rare that I find such perfect solutions to my problems - and can thus improve on my other improvised techniques!! I am not much of a programmer - so I can't turn my ideas quickly and easily into applications (I'm a philosopher!!!). But clearly the people who created Briss and A-PDF Page Crop both new what a user like me was looking for and how to deliver it. I cannot begin to express how much time this is going to save me - and how so much of the work I have left aside (in terms of OCR) for over a year now because I didn't want to crop/divide the double pages [time, patience, and disc space [it took a lot to first save the PDF to image files, then photoshop them into two sets, then reimport them into a new PDF ... !!!!! I was dealing with hundreds of books (which I was supposed to be reading, annotating, and analyzing ... not just scanning!!!!!). Now I can get back to work!