The dead man's switch is a nice idea. 
Thanks, I'm a bit obsessed with that idea
Regarding script.cpp, I just checked if the opcode is there and not the logic. It looked to me that this is not a threshold scheme but a "you must present two signatures" scheme - so that's why I wrote about "increasing risk of loss". Moreover, wouldn't it also have to be used by the sender of the coins?!
I just checked the code again and I'm pretty sure it is a threshold scheme. nSigsCount is the threshold and nKeysCount is the total number of keys. Yes, it would have to be used by the sender of the coins to you. So, either you send yourself transactions like this, or you ask the person paying you to do a transaction like that. This could be as simple as giving them a different version of the bitcoin address that has a few type bits in it and a bunch of concatenated public keys. It would look like a regular address, just longer. You wouldn't even have to specify you want a special transaction, it would be implicit in the address.
An encrypted wallet could protect a user completely compromised by a root-kit trojan. I don't see how cutting and pasting an encrypted wallet over to a service (dropbox) or device (android phone) is any different than splitting keys.
Not if the rootkit has a keylogger in it. Also, it's better if the attacker doesn't get the encrypted wallet, because then the problem is reduced to how good your pass phrase is.