I can get up to cruising speed, from a dead stop, faster and with fewer pedal strokes, on my CF BMC, than I can on any of my steel bikes. If you ride a carbon bike all day, and then jump onto a steel bike, you can really feel the wasted energy that's eaten up by frame flex. For a frame of reference, it's much the same as switching from a fine lightweight steel bike, to a high-ten dept store bike. Talk about wasted energy, about half your power seems to drop into a black hole on dead-flexing dept store high-ten steel bikes.
That said, I still prefer steel, especially for long rides, it's just so much more civilized and comfy. If seconds count, CF is the way to go, but seconds don't count for me, all-day comfort does.