I also enjoy using the Passport Card for the reasons previously posted.

However I do have one concern about the RFID embedded in it because it has been shown vunerable to hacking. Now it is a NUMBER but like a Social Security Number IT is the KEY to all other info about oneself.
ALL Passport Cards and NEWER Passports have RFID's in them and come with a SLEEVE from the Passport Office designed to protect it from unauthorized reading. So they obviously recognize some threat of others reading it.
The SLEEVE is OPEN at the top which would still allow it to be read in some circumstances so I have taken the precaution of wrapping it in the highest guage aluminum foil I could find. This prevents any signal sent out from reaching the RFID and activating until I unwrap it when required.^