When your friends and you have a race every weekend in the summer it is easy to dial in. Come fall and winter, chasing the blue line in the pool and riding the trainer gets old. Redefine what a good month is for you as an athlete. Measure success by the number of scheduled training sessions completed in full (yes, you should still have a training schedule this time of year), your body weight/composition, or simply how you feel.
You can still quantify your success too. Find smaller races to compete around town, like 5k and 10k runs. Talk to your LBS about using one of their Computrainers for a monthly virtual time trial with your friends. Or, organize a simple unofficial foot race with your friends on your favorite route. Handicap the start times based on ability and put a beverage on the line as the prize for the winner. Remember, sometimes fall and winter training is more about entertrainment than hard core training.