For as long as many of us can remember, high-tech industries have flourished in the suburban office parks that are so ubiquitous in Silicon Valley, North Carolina's Research Triangle and other "nerdistans." But in recent years, high-tech has been taking a decidedly urban turn.

Silicon Valley remains the world's pre-eminent center of high-tech industry, of course. But even in the Valley, denser, more mixed-use and walkable places, like downtown Palo Alto, are becoming the preferred locations for start-ups and smaller firms....