Answer:
It's really subjective. I've heard a lot of figures used. Are you talking about homes? are you talking about "people", including their jobs (industrial, farming, etc.)? What part of the world are you in - is the climate hot, cold (this impacts heating and air conditioning loads), or is it just nice all year round?
I've heard a rough figure of 1kW per household, but when wind farms are announced I've calculated their figure to .5kW per house as well, so there seems to be a lot of leeway.
1kW = 10 100W lights running, to put this in perspective. I've measured my George Forman grill at ~1kW (but it's only on a few minutes), Hair dryers and small space heaters can quickly get your house usage above 1kW for a period of time. But that doesn't mean all your neighbors are using similar appliances at the same time (but then again, maybe they are). So time of day may impact how much 1 megawatt will power - at 12PM, it might power 10,000 homes, but only power 500 at 6PM when everyone is making dinner, running laundry, and running the air conditioning/heating.
Farmers that irrigate, and use electricity to run their pumps can be significant load. Industrial plants can also pull a lot of juice, such as arc furnaces used for smelting. I know of some such plants around 100MW, which employ around 500 people per plant, so if you include jobs this is 1MW per 5 people employed.