One of the things that impresses me most about the Inc. 500, and now the Inc. 5000, is how many jobs these companies create. They are truly fueling the growth of the American economy. This year's Inc. 5000 companies employ 942,224 people. And many of those jobs were created in the last four years. (For more data points about the Inc. 5000, including the total revenue and median annual revenue figures, go here. There are also interesting results from our Inc. 5000 CEO survey here and here.)

For our Inc. 500 special issue, I interviewed Charles Hallberg, founder of MemberHealth, this year's No. 1 company. Just five years ago, his company employed 13 people. Now, Hallberg employs 157 full-time workers and hires hundreds more subcontractors. As you might expect, MemberHealth, which manages Medicare Part D prescription drug coverage and processed 52 million prescriptions last year, has gone through a lot of changes recently.

Hallberg gave a lot of credit to his employees for being able to roll with punches. At MemberHealth, an employee's job today might be different than the one he had three months ago and the one he will have three months from now, he says. "For the last couple of years, every day has been get up in the morning and run 100 miles an hour," says Hallberg. "This has put all of us under tremendous pressures. Change can be difficult but also very exciting." Exciting, he says, because it opens career paths and opportunities for everyone at the company.