So I'm working on a new web app I'm at the point where I'm writing the account UI. Is it SIGN IN / SIGN OU LOG IN / LOG OUT? What do you use? (Help me procrastinate...)
I don't show it at all. I try to streamline users into tricking them to join up.<p>I display all functionality out right, give them as much access as I can, and when unauthenticated users try to activate functionality they are lead to a registration page using Facebook Oauth.<p>When working smoothly you only need 2-3 clicks to have a users registered onto your site if they are already logged into Facebook.
The problem with "Sign In" is that it reads a lot like "Sign Up" (another common web site expression).<p>Consumers should be accustomed to Log In and Log Out (e.g. on Mac OS X the Apple menu says "Log Out [user name]..." and the user menu has a "Login Window" item).
Sign In. Like you, I was ambivalent. I went with Login. Surprisingly, a couple friends, who don't take a particular interest in tech stuff, mentioned to me that they'd prefer Sign In, so I switched it. I still don't think it matters much.