Launching my 2nd app on the Mac App store this week and am playing with a new custom UI for the login/Sign up window.
The interaction is such that in a single form you get both sign up and login.
If you fill out your name, then it assumes you want to sign up and the sign up button lights up - pressing enter at that point would also sign up.
If you skip name and put email and password then login lights up and pressing enter at that point logs you in.
The eye icon shows your password in text, and the ? icon submits a forgot password reset form to your email.
Anyway, the app is in review right now, hopefully going live soon!
You can watch a demo video of it here: http://www.vimeo.com/28844803
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