I've had 23s on my bike for a while... I changed them back to my kevlar lined commuter tires 28, which are little less than 100g heavier each. I thought they wouldn't make much of a difference, but I did some hill repeats with a friend and got my butt kicked. Could be a placebo effect, but I felt like the wheels were heavier, slower to accelerate, and slower on cornering.

I switched them to 25s and rode a bit today. I couldn't tell much of a difference between the 23s, but I also didn't bike very much.