ISPs will ignore Google Fiber at their own peril. MarketWatch’s Nat Worden writes that many cable executives he talked with four years ago were openly dismissive of Google’s chances of succeeding as an ISP because the company didn’t have the experience managing a network and dealing with customer service to make it work. Now, however, Google Fiber is up and running in three markets and is considering an expansion to nine other major metropolitan areas encompassing 34 cities and towns, meaning the time for Comcast and Time Warner Cable to scoff at Google’s broadband adventure may be at an end.

“Analysts have crunched numbers suggesting Google Fiber should be taken seriously,” writes Worden. “Evercore Partners, an independent investment banking firm in San Francisco, has predicted that Google could sign up 3 million customers in the next seven to nine years, which would rank it among the nation’s top-10 providers. That’s really a reflection of how few providers there are and why consumers are starved for new options.”

What makes Google Fiber so potentially potent, however, isn’t just its own network but what it’s inspiring other municipalities to do. Many cities with “Fiber envy” have started working on ways to build their own municipal fiber networks, much to the chagrin of incumbent ISPs that have been lobbying state legislatures to bar municipal broadband networks. ISPs can try all they want to delay the inevitable but the fiber genie has already left the bottle and it’s not going back in anytime soon.