Operating under the theory that celebrities are money magnets, America's largest companies have long stocked their boardrooms with a ration of star power. Nancy Reagan was a director at Revlon, Neil Armstrong at USX, and Sidney Poitier at the Walt Disney Co. Michael Jordan is a director of sunglasses maker Oakley Inc.; Colin Powell and Al Haig both sit on America Online's board; and opera singer Beverly Sills has a seat in Time Warner's executive conference room.

There must be something to this practice because far smaller companies are now bringing celebrities on as directors and for advisory boards as well. Drugstore.com has enlisted Martha Stewart and Kim Alexis. Essential.com has tapped former White House chief of staff Samuel Skinner.

Sally Ride, the first American woman in space, says small companies approach her fairly regularly about board posts. She currently sits on three -- which is quite enough, she says, given that last September she took on the president's position at one of those companies, Space.com. "I've found that I quite enjoy boards," she explains. "I like both the people I'm on boards with and the meetings we have."

But do big names bring real value to a growth company? "When I see a famous name on a board, I'm not impressed," says Robert E. Mittelstaedt Jr., vice dean and director of executive education at the Wharton School. "Internet companies need board members to help them build a business model. Plus, a small-company CEO needs and requires good advice because he probably has a smaller management team and needs a board that adds value."

Mittelstaedt's Wharton colleague Michael Useem, professor of management, disagrees. He says that a splashy board is a way of distinguishing one start-up from another in a crowded space. "A celebrity can serve on only so many boards," Useem says. "A start-up that has one on its board can say it's beaten out the competition to get someone everybody else wants to get."

He also sees a famous name as a draw for other board members. "Why do directors want to spend time at board meetings?" Useem asks. "One reason is that they like the people they meet. And who wouldn't want to sit next to Beverly Sills at a meeting? A celebrity brings life to a room."