NRO's Jim Geraghty enlightens:

Smith is a bit more tied to right-of-center political causes than one might initially think. He's a member of the Business Roundtable and the Cato Institute, and is co-chairman of the Energy Security Leadership Council. (John Judis denounced Smith in his book The Paradox of American Democracy as an example of a politically involved business leader who embraces "a kind of irresponsible individualism.") He served as chairman of the U.S.-China Business Council and the French-American Business Council, was co-chairman of the U.S. World War II Memorial Project, and served on the boards of the St. Jude Children's Research Hospital and Mayo Foundation...

While Smith's life story and hands-on experience managing a large, successful corporation in the era of globalization would be a lovely addition to any future administration, Smith's potential flaws as a running mate are clear. He has never held elected office, nor sought it, which would complicate the "experience" charge used against Obama. He speaks with a light Tennessee lilt, and comes across as brainy and soft-spoken in interviews. But it remains unknown whether that style would be effective on the campaign trail. Could he be an attack dog? How would he handle a slick jab from, say, Sen. Joe Biden in a debate?

Most observers think McCain needs some flash in his running-mate pick, someone exciting and different. It's one reason why McCain's veepstakes includes more long-shots and political neophytes like Smith.