Mailchimp - Reduces your price if you use two-factor authentication.
Mailbox - The app categorizes emails from your own address as “Note to self”
Sugru - Lets you look at the most recent issue of their newsletter before actually signing up for it.
Kickstarter - The email sign up field proposes related email provider is it thinks you may have mistyped your email.
CSSHat - After purchasing and downloading CSS Hat, it adresses you by your email in the installation process.
/via Jonathan Shariat
Facebook - If you try to log in with a wrong password, Facebook will send you an email with an Instant Login link.
/via Hannes Struß
Basecamp - When you copy-paste an email ID like “John Doe <firstname.lastname@example.org>”, it automatically strips everything and leaves just the email address.