I just finished the RFID project as described in the Practical Arduino book. After much headache I found slight differences I though I might document for future reference and in an attempt to save others from hassle.
the LED schematic is generally wrong both in book and their website, the indicator LEDs should be wired: 5v ---- resistor ---- >|red LED, Pin 13, resistor ---- >|green LED ---- ground
the sketch as found on GitHub and other common websites is relative to older releases of Arduino IDE (1.0 won't wort, I used alpha 0022)
In the code Serial.Print(tagbytes[5], HEX) should be changed to Serial.Print(tagbytes[5], BYTE) or serial monitor will display HEX for the value of the card
hope this helps someone, I searched the web without any answers until noticing the difference in IDE releases