I have been commuting for the past two months to work (7 miles each way, but I often increase the distance to 12+) on my hardtail. Due to the fact that my rear tire was starting to show wear, I have been considering purchasing a road bike for the commute which is mostly on paved trails. Since I didn't feel like spending the money at this time, I decided to purchase some road tires. I swapped my Kenda Small Block Eights for Serfas Barista LT 1.25" tires.
My first ride to work was 25 miles (including a rail-trail) and all I can say is WOW! I could not believe the difference in my speed. Granted I have to increse my rpm's to get equal speed, but it is a tradeoff I am willing to make. Riding home last night I increased my average speed by almost a full mph versus my previous record and I definitely was not riding as hard. Today I had a 12-15 mph wind with gusts up to 20 and it seemed like it was easier to pedal, even though I despise a headwind. I am normally a dirt trail rider after all.
I will likely purchase a road bike for the commute, but in the mean time I was definitely impressed with this swap.