It is interesting to see the current results with over 40% in "Sorry I can't help, but I just can't recall any ..." but I expect most of these people will not realize how much pressure you may get from legal authorities to release your password. Chances are most of you would crack after you have legal authorities pressing you. Why? because you don't need to be criminally prosecuted for your life to be made miserable. Especially if you don't have anything incriminating, it will be easier to give the password show that you don't have anything and just go on and change your password. Now this isn't fair and we should have legal protection against officials for even asking the question, but real life, if you are going to stand up for your rights, there will be consequences you will have to face. If you have the bravery to do this, good for you. But in reality most of us do not have the bravery that we think we do in such a poll.
That depends on how you assign passwords in the first place. Myself, I've hit a point now where nearly all of my passwords are uniquely auto-generated, and dumped into my keychain. I never even see them directly -- the process is pretty much automated. I didn't generate them, thus I don't know them.
Thus, if for example I were travelling and a government official or someone in a dark alley wanted to know my Facebook password, I can't help them. I don't know it. They interrogate me or hit me over the head all day and night long, and they aren't going to get anything. This is why, when I travel to the US, I don't take my keychain with me.
Now local authorities who can force me to sit down at one of my primary computers to unlock the keychain are a different story, and not one I could do a whole lot about. At a minimum, they could certainly compel the keychain password out of me and do it themselves. The key (no pun intended), however, is they need the keychain in the first place to do this.