Actually, this can be broken down a bit more: How many people do you want or need to hire directly? And how many net jobs do you think your business will create/destroy in the larger economy?
How much does your business's impact on employment influence your thinking and day-to-day activity?
My first business, a web development company will likely max out with 5-7 employees. My next, a jobs search site may involve a workforce of 30+.
Ultimately, I want to build a company that has a large social impact like FB. That's maybe ten years, a few billion dollars and 1000 employees away so no further comment needed. =)