Gigantt - When you estimate a task using free text you see a live preview of how the system is interpreting it.
/via Assaf Lavie
Facebook - The prompt text in the “Update Status” field constantly changes on refresh.
/via Ahmed El-Agha
Simple - While signing up for an account, a Visa debit card is filled with your name as you type it in the form.
/via Tyson Gach
iCloud.com - Removes the spaces from the email input field when you go to the password field.
/via Andrey Usoltsev
Square card case iPhone app - Credit card form that shows card type and flips around when you get to the security code on the back.
via Matt Bilson
GetSatisfaction - Gives instant feedback when using too many capitals in your title.
YouTube - If you are not logged in, the “respond to this video” textarea asks you to Sign in or Sign up on mouse-over.
/Via Marian Buhnici
Ta-da Lists - Remembers the username / email you entered and pre-fills it on the “forgot password?” page.
/via Caleb Lyons
Mailchimp - Makes you write the word DELETE if you want to delete a mailing list.