I've seen a number of 12-week 5K training programs (Pete McGill's is one.) They all gradually increase speed work as you approach your goal race. My question is, what happens after the race? Do you choose another goal race and repeat the program, but now at presumably faster paces?
Another way of asking this is, how does the year-round runner use training schedules, and how many goal races can you really have? How do you treat intervening 5K races?