Steve Coe gives the GNU Emacs Pocket Reference a "thumbs up" for
handiness, but notes this is a title better suited for jogging the
memory than learning everything there is to know about what Neal
Stephenson calls "The Thermonuclear Text Editor."
"If you're serious about learning Emacs and money is no
object, I would say to check out Learning GNU Emacs first before
picking this book up.
If you're short of cash however, or just want a handy reference
to sling in your backpack or pocket to help steer you where you
want to go, or if you're a hardened Emacs veteran who occasionally
suffers brainfade, the "GNU Emacs Pocket Reference" is a terrific
little book. Highly Recommended."