As Greg LeMond said, "it doesn't get any easier, you just go faster."

After a year of holding myself to my aerobic limit while riding and pushing a bit past it on my 7 mile round-trip commute, I now cruise at about 18 - 22 mph, depending on my cargo load, headwinds, pavement conditions, etc. I've held a nice comfy 25 mph on fresh pavement with a tailwind. I think my record is around 28 mph on a flat.

It's really the acquisition of a road bike that ruined me. Before that I was quite content to go much slower while wearing regular street clothes.