How Twitter could be a threat to Google

[Commentary] Google's search engine is so dominant that it's hard to imagine how anyone could knock the Mountain View company from its pedestal. And yet if history is any guide, such reigns never last. IBM gave way to Microsoft, which now has been usurped by Google. It could be a shift in technology. It could be a more nimble, innovative rival. But something always comes along and turns things upside-down, often emerging from a direction so surprising that the incumbent never sees it coming until it's too late. In this case, it's hard to imagine a company that might post a more surprising threat to Google than Twitter. But just this scenario is suddenly generating some heated discussions around the Web.