I am one of the person convinced that a computer disk encryption system will not protect you from public authorities if they are convinced enough and the case is very important.
There are a lot of way to convince a person to release a password.
However there’s a case in Australia where not revealing the disk password resulted in a successful way to avoid going in jail:
My opinion is just that spying flatmates is not a so relevant and particular crime and that law enforcement did not used ‘convincing systems’ to get the password of encrypted disk.
UPDATE 29.06.2010: It also worked for Daniel Dantas against FBI .