I just moved my encrypted HDD out of my Thinkpad and connected it via eSATA to my desktop realizing, that my desktop did not manage to see the data. I totally forgot about the harddisk encryption here. The scary part is, that I thought the drive is damaged, because both, Windows and Linux were telling me, that the drive is broken. Linux beeing more informative said, that the drive did not understand my commands, so I thought the firmware is broken. I could not even write a new partition table or else. Same with USB to SATA adapter by the way.
The encryption on the Thinkpad is quite fast (1-2 seconds to enable/disable), which made me think that it only encrypts the partition table, but it seems it is overwriting some part of the drives firmware. Quite bitter if you forget the password, because your drive is wasted then. On the other side, all the information is still set plain, if it only encrypts parts of the firmware. Maybe it uses some harddrive specific algorithm, too (its a Western Digital), but I am not sure.
Anyway, quite cool that my drive is not broken. Hopefully it stops 90% of the newbish attackers :)