Chris commented on my previous entry regarding the fact that Floria is faster than the Castafiore was:
My guess is your new bike has lighter rotating components.. especially the rims. These are probably solid on the old bike and are hollow on the new.
This is a mixed blessing: the bike is faster, but the rims wear out faster!
Removing weight from rotating components has twice the effect of removing weight from the frame when accelerating. Acceleration is probably a key issue in your ride to work.
The bearings are probably also improved... below about 18 kmh rolling friction dominates.
I respectfully disagree with Chris' main point. Floria was designed as a cyclo-cross bike. As such, she was built with fairly robust components. On the other hand, the Castafiore was designed as an entry level road bike but in the course of various upgrades, received rims of near touring-grade quality. Thus the rims are probably very similar as are the tires. In fact, the front tire on Floria came from the Castafiore! (The rear one had to be replaced as described in this entry.) Therefore, I doubt that there is a significant difference in the rotating components between Floria and the Castafiore.
However, Chris' point about better bearing may be valid. Although the number of times the wheels on the Castafiore were changed is significant, bringing the possibility of incremental improvements to her bearings.
My take is that it is the improved shifting components that are responsible. Moving from friction shift levers to brake-shifters is a huge leap forwards. On the new bike, it is very easy to accelerate in low gear and then pop into high gear with little thought or worry. The process of shifting is faster and much predictable. Consequently, acceleration is faster than before. Faster acceleration equals higher average speeds and thus a shorter commute.
As well, the ease of shifting means that the new bike is more energy efficient which translates into less fatigue and a greater ability to apply power later in the commute. This also leads to the shorter commute.