Hi Mike:
It will look the same...but smaller
Seriously, you may want to print out the PDF with an appropriate page size to simulate the Reader's screen. That should give you a good idea of what you'll get.
If your PDF's have been formatted for the smaller screen, they will look fine. If they are formatted for regular paper (8.5x11 or A4) they probably won't work to well.
Cheers,
Bob