I feel kind of obligated to mention that you can also solve the same problem if the machine is sitting around fully unlocked (not idle and thus cluing the disk

I feel kind of obligated to mention that you can also solve the same problem if the machine is sitting around fully unlocked (not idle and thus cluing the disk encryption in) with a cold-boot attack -- http://citp.princeton.edu/memory/ http://citp.princeton.edu/memory/ . The short version: the contents of RAM are preserved pretty well during power loss if you cool the RAM chips, e.g. by dunking in liquid nitrogen or even just spraying with an inverted air duster, and the encryption key is stored in RAM so that the intended user can access the disk, so you can later recover the key from the frozen RAM.