Hmm. They were there yesterday. And they're up and okay on the website.
No, they weren't there yesterday either. I'm a bit depressed because it probably means my 12 billion point game of Twilight Zone won't post to the leaderboards. I guess it could be worse, some people are reporting losing access to their (in-game) purchased tables. BTW, the leaderboards still appear on the website and on the Android version, so it's definitely a problem with the Steam version.