Originally Posted by Gatorfreak

For the last 7 months I've been riding the 700x30 Kenda Kwicks that came on my bike. They are slightly knobby. My best commute home was at 18.5 mph average.

Yesterday I rode my new tires (700x28 Forte Strada K) for the first time. They are slicks, or close to it. I averaged 19.3 mph on the way home with no significant wind.

As the title says, not very scientific. But such a jump from my previous best would indicate that it really does make a big difference.