The arrow labeled "subjects" in the diagram should have a black ball
on the end.
3rd Printing (May 1995)
pp 297
"...to let the observer know which observer is sending
the notification."
should be
"...to let the observer know which subject is sending
the notification."
2nd Printing (December 1994)
pp 12, inside-back cover
The "spaghetti" diagram changed slightly to include an arrow
labeled "sharing states" from State to Flyweight.
pp 175, 195, 196, 202
Some lines on these pages did not print correctly. (Well they
did, but with width 1 at 2200 dpi. If you squint really carefully at
your copy, you might just be able to see them!) Here's what they should look like (24KB
PDF).