[shangxiao]

Along similar lines, I detest a trend I've noticed where login forms show the username/email & password on separate forms. It's annoying to have to click through more than is necessary and additionally breaks my password manager's auto login.

[thanatropism]

Tumblr has done this for how long?

Worse yet, they have very similar (except for color) buttons for "Log in" and "Sign up". Often if you have bad internet and the last layer of the page hasn't loaded yet, you don't know which button to press.

[ge0rg]

The worst offender here is Microsoft, if you have a personal and a business account under the same email address (that alone is a major UX fuckup). But they add insult to injury by showing you a typical email+password form, and when you press [Tab] after the email address and start typing your password, the form is replaced under your eyes with a dialog to choose which account you want to log in, only then followed by a password prompt.