This community inspired me to do some craftsy projects over break, so I made several book boxes and really enjoyed it. It's a neat outcome too!
The best tutorial I found was at WikiHow: http://www.wikihow.com/Make-a-Hollow-Book
Some things I found useful:
Old Reader's Digests have pretty covers and occasional nice pictures inside.
A sponge works just as well as a brush.
Drilling holes at each "corner" makes that 90 degree turn much easier.
Clasps are really cute additions to make it more "box" like and I glued pictures on the bottom inlay of the box.
I found the bigger Exacto knives do the job quicker and with a decent amount of precision.
Some finished products:
Sorry if the pictures are too big. My LJ cut function disappeared...I will resize if necessary.