It would annoy the heck out of me.Wonder if that would cheese me off on a commute? Every ride your 'best' time is ahead of you and you either can't be arsed or have the elements slowing you would be frustrating to say the least.
I commute on my cyclocross bike 99 times out 100, but every so often I'll stick my suit in a rucksack rather than my panniers and give it a blast on the carbon. Did it yesterday and was 5 whole minutes quicker on the way in than the day before and probably 2 minutes quicker on the way home. There's no way I could ever match those times on the normal bike - So I'd forever be chasing unrealistic targets.