Par4QC I'll go back, at least 15 years, and state I have only seen 1 person in that time, carrying his bag. That was in a AmTour tourney I was in and he held up 4 groups in carts.
Different culture over here - from what I've seen, more people are using push carts/trolleys now than in the past (and a good proportion of those are using powered trolleys), but at least a third of the golfers I see on the course are carrying their clubs, and it doesn't affect pace of play. It's also pretty rare for me to see a cart out on course (and there's usually a medical reason for that person to use one), particularly at this time of year - it's cold enough to walk a round of golf when the temperature is in the mid-40s or lower, and it would only be worse if you weren't walking...