We're in no hurry to start potty-learning, but I decided to buy a couple of cheap IKEA potties and stash them by the diaper changing stations just to get Carter used to their presence. At diaper changes, we occasionally let him sit on the potty. He has yet to do anything other than sit on it, but we're not really expecting him to any time soon.
Here is a video of him playing on the potty. In the beginning, you hear him say "in, out" -- he's opening and closing his knees. He likes to do that with his feet, his arms, and so on. "Old McDonald" is playing in the background and he does a little singing along!
And here's one more picture, one I just thought was funny: