A growing number of Americans have home Internet speeds that make your broadband connection look like dial-up.

Ultra-fast Internet is quickly spreading across the United States. By fast, we mean gigabit-per-second speeds, roughly 100 times faster than the average home Internet connection.

There are now 27 U.S. cities that offer gigabit Internet speeds to consumers -- up from just two cities as recently as a year ago.

AT&T (T), Google (GOOGL) and CenturyLink (CTL) have been the main drivers of ultra-fast Internet for home customers.

Google was a pioneer in the field, bringing its Google Fiber service to Kansas City, Kan., in 2012 after holding a widely publicized contest two years earlier to pick the launch city. Fiber has since spread to Kansas City, Mo., Provo, Utah, and will soon launch in Austin, Texas. Google has announced plans to bring Fiber to nine other cities across the country in the coming years.

AT&T's U-Verse service has been most bullish in its gigabit Internet plans, launching or getting set to deploy in 14 cities over the past year -- including major metropolitan areas, such as Dallas, Charlotte, Houston, Miami and Nashville. It is currently operating in Dallas, Fort Worth and Austin, Texas, and it is exploring gigabit Internet deployments in more than a dozen other markets in the future.

Broadband provider CenturyLink is launching in 10 markets, including Denver, Las Vegas, Orlando, Salt Lake City and Seattle.

Related: New Internet speed record blows past Google Fiber

The companies say that super-fast Internet speeds will help companies create the next big innovations that we can't even conceive with our current speeds. For instance, no one would have believed that YouTube or Netflix (NFLX) could have existed in the days of 56k modems.

Although gigabit Internet hold great promise, the use cases for it today aren't vast. Most content companies simply aren't capable of serving up websites, photos or videos as fast as gigabit Internet users can download them.

For example, Google Fiber customers only receive Netflix videos slightly faster than Cablevision (CVC) subscribers -- who have nothing close to gigabit speeds available to them.

As gigabit Internet spreads across the country, however, content companies would likely be forced to make use of those capabilities.

But it's not certain that every city in the United States will get gigabit services. Super-fast Internet requires fiberoptic connections to be brought into a customer's home, which can be a very expensive endeavor. As it stands, the gigabit Internet roll-outs today aren't happening in every neighborhood of the 27 cities.

The good news is that broadband companies are increasingly testing ways to send super-fast Internet over their existing copper-based infrastructure. They hope one day to deliver gigabit Internet to customers' homes over landlines. But the technology is still experimental.

So if you're not one of the lucky few to have gigabit Internet already, don't hold your breath -- but don't lose hope either.