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…
I could not agree more with the points you mentioned. To solve the last one I added the option to create an encrypted list for the sites. But so you end with an additional password you need to remember because using the same as for the masterkey makes this the only key to access every password. And this is what the system tries to avoid.