I've had my clipless pedals for a month, so I'm still very new. But here's my experience, for what it's worth.

I went straight from platforms to clipless. I still have to tell myself to unclip at times, but the more I ride, the more natural it's becoming. I had some difficulty getting into the pedals at first (there's a thread 'round here somewhere). It got much easier. Occasionally there's still a bit of "hey, where are you? Clip in, dammit...Okay, thanks...Oh, a stop sign. Grrr." on my rides. (Yes, I talk to myself while riding...) I attribute this partly to my getting used to where the "spot" was, and partly to the newness of both cleat and pedal wearing off.