I did some googling and the part of copy/paste of public key to website is pretty obvious and could be useful maybe for some tech sites. At least many people can do copy/past of key very well, as you can see by trying to find all public/private keys at pastebin.com ...

But what is very difficult is to enable website to authorize using your agent or your private key. But ... the SSL certificates in browser should be the way to go, but as author in blog post wrote "they are just so full of glitches and surprises as to be virtually unusable" :-(