A self-destroying drive would likely get you a conviction for obstructing justice, just like shredding the contents of a safe would.
Disclaimer: I am not a lawyer. Most of what I know about this is from the last twenty minutes of googling.
In 2007 a federal judge ruled that passwords aren't like keys to a safe, and that the government can't force somebody to hand them over. (United States v. Boucher http://news.cnet.com/8301-13578_3-9834495-38.html )
However, that decision was partially overruled in 2009. ( http://www.bennettandbennett.com/node/5608 ) The judge ruled that the defendant didn't have to provide his password, but he did have to provide the contents on the hard drive. In other words, if the defendant happend to have an unencrypted copy of the hard drive hidden away somewhere he could have offered that in place of the password.
Using your safe analogy, it would be like saying that you don't have to provide the government with the key to the safe, but you do have to provide them with an identical copy of everything contained within the safe.
Now, like me you're probably wondering how the government could prove that the contents you provide from a secondary source really matches up with what's on the encrypted drive. The Boucher case mentioned above was unique because border control agents had already viewed the contents of the guy's laptop in unencrypted form, so they knew what to expect. (In his case, child porn.)
From what I can find, there don't appear to be any laws in the U.S. (and no case law) which specifically require people to hand over their passwords at the government's request.
Here are two more links I found which were helpful: http://volokh.com/files/BoucherDCT.1.pdf and http://en.wikipedia.org/wiki/United_States_v._Boucher
Encrypted data isn't so clear cut. It's trivial to make a datastore that has several encryption keys, so that you could give out one key, and it'd "decrypt" to some boring stuff, whilst keeping the real data, and the alternate key, secret.
It'd also be trivial to devise a decryption algorithm, and key, which "decrypts" anyones hard drive to reveal illegal images even when none are really there...
So I don't think it's a good analogy. It's quite obvious when you have successfully got into a safe, but how do you know when you have successfully decrypted something, to the real stuff that is important and being hidden in it?
If we assume the courts can order you to decrypt the drive (and without debating that point) - one has to consider that the court may be fully aware that the system has multiple hidden volumes, either by eyewitness testimony, 3rd party evidence (check out truecrypt's warnings on their site about full system encryption and what to watch out for. Things like finding the same windows installation doing every update twice. There are all kinds of information leaks that COULD pop up.
I'm not saying it's impossible - just as strong cryptography, which is easy and is all over, doesn't mean all our data is secure, neither would a more complex system like this protect someone from the legal system.
You can use one algorithm to encrypt/decrypt the original content. But you can use a different algorithm (with a different key) that would output a different output.
The secondary algorithm would be one that given a some text (ciphertext from the original encryption) along with the desired output, would return a suitable key. The most basic example to prove the point would be XOR.
If you give a password, the cops will know what algorithm they must use (2 trials at most). Even if they don't know before hand which algorithm points to the real data, they can notice that it doesn't use all data.
With your method, you can at best cast doubt: is the data not extracted real data encrypted differently (algorithm or key), or random data that the software insert by default to give everyone plausible deniability?
http://en.wikipedia.org/wiki/The_Mystery_of_Al_Capone%27s_Va...
Well the revealed images could not be significantly larger in size than then the "key material" you supplied plus the most concise description of the algorithm. http://en.wikipedia.org/wiki/Kolmogorov_complexity
How trivial? Remember that the whole hard drive must be consistent, including a file system. Fifty gigabytes of garbage followed by a 2-megabyte photograph followed by fifty more gigabytes of noise is not plausible.
What level of data protection counts as contempt or obstruction? What if I have provided the courts with all of the data, but for some reason they suspect there's more that I'm hiding? What if I honestly can not remember the password for some of my old data? Do I go to jail because my memory is gone?