I’m the last person in the world to have much of anything to say about visual design, but this one is so blatant that even I can’t help but notice:

See the big blue button in the same place? In one case, it is a ‘sign up’ button, in the other it is an ‘enter if you already have an account button’. This is visually confusing for those (and there are a lot of us, I’m sure), who use both products.