Rent the Runway's slogan might as well be: Friends don't let friends wear H&M to the most important events in their lives. The company solves the perennial "closet full of clothes and yet nothing to wear" problem that most women face, by allowing them to rent designer clothes for a big event for about 10% of the price. It's clearly a problem women have. The question-- like most rental businesses like Zipcar-- is how many women want to rent clothes as the solution. So far, there's at least one million active users, spanning a wide demographic of women, from 15 years old to 45, says Jennifer Hyman, Rent the Runway CEO and cofounder. "That was a surprise," she says. "Initially we thought it would be only young women in their 20s."