Well I've been using the clipless pedals for a week now, and in that time I've done quite a bit of riding in a variety of styles.
I have done one long ride, several standard commutes and a couple of pootles.
I can confirm my initial thoughts in that it still makes cycling feel easier and I now thin I know why. I'm sure there are forums dedicated to this so I am sorry for repeating the acculated knowledge of the interweb. Being clipped to the pedal encourages smooth actions as you can feel whether you are pushing evenly as the shoe tugs at your foot if gets ahead of the pedal.
On long rides I really noticed less fatigue and a willingness to power out of situations more often. Anyway I think they are here to stay.