I'll share my experience in using PDFCropper for the jetBook. So far it has turned out to be a great help!
A bit of background: There are a few authors I like who have been releasing free versions of their books as downloads online. Unfortunately, they are only in PDF format -- mostly because they are scans (or perhaps PDF exports) of the books. As such, they don't work too well on the small jetBook screen. If I have it in portrait mode, the font is very small. In landscape, it's OK, but requires lots of scrolling. I don't like scrolling because over the overlap of lines... every time I scroll I have to mentally readjust to find my spot. Page turns are much better.
I had compensated by trying a bunch of free PDF tools, like PDFill and PDFSam. These let me crop, rotate, etc. the pages. So for a typical book, 5.5"x8.5", I would have to crop out the margins, the headers, etc. by trial and error. Then, I would create two copies of the book and cut them each in half... a top half and a bottom half. Finally, I would use a PDF merge to combine the top and bottom halfs, alternating pages... essentially leaving myself with 'half-page' turns. I used Full Page zoom with white cropping in the jetBook itself.
This worked OK but 1) It was tedious, 2) It lost the table of contents and 3) It created files double the original size. So I was very happy when I found that PDFCropper can do the whole thing in about 1-2 minutes instead of 10-15 min. per book. Actually, most is automatic, with me just waiting for it to finish its job.
Here's what I do for my PDF's in PDFCropper:
1) Adjust the gray lines around the PDF as the Frames Area to exclude headers and footers. I put them very close around the text, but not too close on the left or right, since odd/even pages are spaced differently. PDFCropper can actually handle these, but I don't have to worry about it since the jetBook can crop that white space.
2) Go to Edit Menu and run Auto Frames. This process takes about a minute and with its default settings nicely frames two halves to each page. For some books I might use thirds.
3) Then File Menu and Crop to crop into a new PDF! This takes a few seconds, and also lets me set the Title/Author information for the jetBook display.
Quite easy! I like the PDF result because it shows the original text as it appears in the real book. There is also a reflow option, which is quite decent! But I haven't needed to use it much. The Aluratek Libre firmware on the jetBook does support reflow, but it doesn't look nearly as nice as the original text divided into smaller screens.
I also like that if I ever buy another device besides the jetBook, it would be quick and simple to reconvert my PDF's to that device's specifications. It has a lot of features that should work for just about anything!
Hope that helps greenapple!