Typically, we use this column to spotlight corporate-governance trends that are on the horizon and heading toward boardrooms. This time, we go deeper under the radar to find a phenomenon that promises to turbo-charge shareowner activism—and provide new wormholes for executives to monitor dissent.

In 2007, blogs, bulletin boards, and email blasts have reached a critical mass among investors. That “B-List” has powerful consequences: the stately pace that once marked the procession of dissident shareowner campaigns from a gleam in the eye to annual meeting threat is now hugely compressed. The Internet has put shareowner activism on fast forward. Plus, ...