P300 has been around quite a while in psychophysiology, turning it to terrorists sounds like a possible beat up to meet priority funding by NIH or similar? though they just might be onto something if the implementaton issues could be sorted.
Implementation wise OK lets see its usually a 20min setup to get the electrodes on the 'perps' head, then sit them into a shielded room, get them relaxed and get them to not move around too much as muscle movement artifact washes out EEG signals. Now put them through a few hundred trials of questions and answers so you get statistical validity, process a few GB of data and hey presto an answer.
FWIW I hope it doesn't become a part of airport security routine checks ;)