i think that depends on the strain though doesn't it comrade? i've veged my plants to 4 or 5 feet and then flowered them, and they didn't grow much more. then again, i let them veg until the plants had finished their natural cycle. the growth was very random, pre-flowers were abundant, and they kept telling me "go 12/12, go 12/12"
disclaimer: i only have two grows under my belt. while that does provide some experience, i still have mountains to learn...