http://en.wikipedia.org/wiki/United_States_v._Boucher
In February of this year, the judge required him to provide unencrypted access to the drive.
(But of course, if you are at the point where your hardware is being seized, it's possible that the government already has enough evidence on you.)
I it could be argued that pleading the fifth for every single question is allowed under the Fifth Amendment because what information you think might be incriminating is also incriminating information. AKA where on December 2, 1952 and you plead the fifth. But you are willing to say where you where on the December 1, 1952 and December 3, 1952.
In the UK the government settled the question with a law making it a crime to withhold your password:
http://security.homeoffice.gov.uk/ripa/encryption/faqs/
The issue hasn't really come up in Canada. Some authorities have recommended a law similar to the UK's.