maddog,
Your test results will tell the tail; if you have combined chlorine over 0.5 ppm then you need to shock. In situations like you describe though, I usually start the party with a little extra free chlorine in the water (8-9 ppm with CYA of 30 ppm) and dump in another jug (another 3.8 ppm) at the end. The next morning (or afternoon if it was a really good party), my free chlorine is usually in the 4-10 ppm range with no CC. Occasionally, especially with kids' parties and all that they add to the water (hey, has anyone been to the bathroom in the last 4 hours?), I can smell what I assume are chloramines but I have no CC by the next day.
Like waterbear said, it's really a function of how well you stay ahead of the water.