Others have expressed most of them, but issues I see with this is: * Algorithm can't be changed/improved without changing all your passwords. * Your master password can't be changed without changing all your passwords. * You have to remember yourself at what sites you are already registered, and in case of critical bug, you would perhaps need to change password at some services (again remembering which ones they were…
If you compare this to two factor authentication it's the same amount of extra work, but without the benefits.
You should also avoid copying passwords to the clipboard as many applications and even web sites might have access to it.
Too bad client certifications are deprecated, now when SSL/TSL is becoming more and more popular. Only downside with client certificates is that you have to copy the key (witch can be password protected) to all your devices. Another downside was that the site required SSL/TSL, but almost every site have that now!