I am surprised at how little we discuss having riding groups, such as clubs. I started riding one year ago. For the first four months I rode alone in the parks and local roads on my hybrid. I thought I was progressing well. In January 2007, I bought a road bike and in the middle of January I rode my first group ride. It was cold, but not miserable by any means. I kept up for about 2 miles, but with my nose running, coughing, extreme gasping for air and mumbling words that could not be understood, I fell off the group. A very nice lady with the group rode beside me and said she understood. She told me to just stay with her, which I did. I finsihed the ride. It was basically the same for the next couple of weeks as I started to understand how much work I needed to be able to ride with a moderate group. It basically proved that my solo riding was not doing that much good.
I have now finsihed a couple of century rides and can easily stay with my groups. Most certainly I would not have been to this point by riding solo. If you really want to impove your riding and heath, find a group, or two and ride with them. Just my experience.