I currently do 6.9 miles one-way, with a large V shaped hole in the ground at the beginning. The worst part isn't the distance, or even the hill, but the 1.2 miles in the open country along side a 6 lane road. In winter, the wind just sucks until I can get into town. Then of course, I get to deal with traffic. It usually takes me about 35-40 minutes each way, which isn't too bad. As long as I keep doing it, I stay in decent 'bike shape'. It's when I fall off the wagon, or don't ride (like now, with 7" of snow on the ground), that it feels worse. Just keep up on it, get a good saddle, and don't carry anything on your back and you'll be fine.