Thanks, I added a link to your post in the docs

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As for the password thing, yeah: either you use the same key everywhere, and it's secure as hell, in which case you're using an agent to not spend your time entering a long-ass passphrase.
I'm not sure if there's a better solution that Pagent on Windows, but on Linux, pam_ssh rules, and on OS X, ssh-agent ties into the OS's KeyChain.
Or you're using a throwaway key just for the Kindle, and a passwordless one is fine.
Speaking of keys, last I checked, only development version of PuTTy supported ECDSA keys (better, stronger security, and much faster).