For an alternative point-of-view, read Grant Petersen's nifty little rant about cycling shoes and pedals.

What it boils down to is feel. That's such a subjective topic, everybody says they "feel" better, but they do not actually make a measurable difference in efficiency if your pedaling technique is already good. Now, in all fairness, if they "feel better" then you might be tempted to work harder, but the fact is they're just different, not better or worse.