i already thought bitmessage was easier to use than email. installing the program and running it was far more painless than filling out some form to get an email account. if you are going to make it even easier still than that sounds awesome.
You'll have to fill out a form to use Frog, but all it will be is username, password, and repeat password. No existing email required.
i wouldnt make them repeat password and i wouldnt differentiate between account creation and login. just have it be assumed by your server that if someone tries to log in with information that doesnt currently exist than have it create a new account. if they type something wrong they will figure that out when they see that they have no messages in their inbox.
a card game i used to play did this, shadow era. check it out, its awesome how low the barriers are to playing that game. you dont even have to confirm your email, the email you enter doesnt even have to be a real email.
*edit* actually why not take it even further. instead of having username and password just have 1 field (userword?, passname?) i dont see any reason not to.