I'm a noob cyclist with a mere 2800 miles under my wheels. As such, I try to make use of the wisdom gleaned on Bike Forums. I believe BluesDawg is right in that performance benefits can be exaggerated.

I've tried to maintain a higher cadence than initially felt comfortable. Now I pedal at 85 to 95 rpm. I found that at higher rpm, my feet tended to wander on the pedals and needed to constantly recenter them. Now I'm on SPD A520, as BD recommended on another thread, and no longer think about my feet. The shoes are normal to walk in and are comfortable. I suppose clipless is more efficient but at my level it is not a big difference. I do think clipless promotes a rounder pedal stroke so it may be the benefits will increase as fitness increases. Worth the expense - yep.