Everyone seems to be forgetting the real big security issue with this.
Accessing physical data on the system's hdd (whether encrypted or not) is not the major issue - accessing currently running programs is.
Example - John Q Sysadmin has a few open ssh sessions to some of his favourite boxes - locks his workstation so he can wander off somewhere. Anyone exploiting this to unlock his workstation now has access to his logged-in ssh terminals.
Yes, there are other ways to achieve this, including keyloggers, trojans, etc, but this makes it stupidly easy to walk past a random workstation, and potentially 10 seconds later have root access on any number of other boxes the user happened to be logged in as.
Remember guys - better be shutting down your ssh terms before you go to lunch!