Here is what the author had to share on this:
"99% of the contents of the book will work as is. The hardware of the B+
has changed from the B in the following ways:
* B+ has proper (and sanely located) mounting holes
* B+ has a 40 pin GPIO header vs the B's 26 pin GPIO header (though, the
first 26 pins on the B+ are the same)
* The power socket has moved
* There are 4 USB ports instead of 2 on the B
* The Ethernet ports have status LEDs
* The audio hardware is of higher quality
* The composite video moved from a dedicated RCA connector to sharing
the 3.5 mm connector
* It uses a bit less power (3.0 vs 3.5 W, 700mA vs 650mA), and is more
tolerant of power issues.
* The notorious C6 "thumb rest" capacitor is gone.
The kernel compilation from scratch docs should still be completely
identical. The only things that wouldn't be perfectly lined up would be
pictures that point to B specific layout for wiring. But the CPU and GPU
are identical and there are no real code changes necessary to run on the
B+ vs the B (outside of code in the Linux kernel, graphics library, and
firmware, all of which is provided by the Raspberry Pi Foundation)."
see the change log