Why should people spend any effort at all to secure things that shouldn't be secured in the first place? Why should anyone remember a single bit of info or download an app or spend an extra keypress to protect an account that's already public in intent; but "private" because someone else wanted it to be private?

There are security problems if you use your 'throwaway' password for your primary email (as some of the people on Adobe list have done), but that's not the fault of the throwaway password, but in throwing away the keys to something valuable. That throwaway password should be something that's not a secret, as an equivalent to no password.

It should not even attempt to be protected - it's something that you tell your friends/colleagues openly (so that they'd not have to create their own accounts there, it's quicker to login with yours), post it publicly on the internet (again, bugmenot.com as an example), don't bother to change it years after some site has leaked it, etc. The password as such exists only because someone forces you to some tradeoff of "more security/less usability" - the only reason that the password is not, say, a 0-length string is that you're forced to do so, but there's no reason at all to go any further than the minimum.

For the majority of accounts that I have, the most appropriate level of authentification is not "a reasonable level", not "a minimum", but exactly zero.