Until now, Google has had to build Fiber's gigabit networks the hard way, either from scratch or by making deals to use some existing lines. It's about to try something new, though: the search firm is bringing Fiber to Huntsville, Alabama by using a not-yet-finished municipal network. Huntsville Utilities will "design and construct" the fiber optics, while Google and other providers will simply ride on top. There's no timetable for when Google Fiber will be ready (that's contingent on Huntsville), so you shouldn't expect to sign up any time soon.
The expansion to Huntsville may seem odd at first blush when Google Fiber has focused on either large cities or smaller towns with ready-to-go networks. A burg with roughly 180,000 people isn't exactly a lucrative market. However, Google sees this more as a proof of concept for gigabit internet than anything else. Huntsville has an extremely high concentration of engineers and scientists thanks to its biotech and space work -- it could really use those breakneck speeds to shuffle large amounts of technical data.
Also, the use of a city-run network shows that Google is more flexible on its rollout than you might have thought before. It would rather give up control of the fiber cables than risk missing out on a chance to expand its reach. It's doubtful that Google Fiber will become ubiquitous any time soon, but you could see it become a relatively commonplace option in those towns where gigabit-class municipal broadband exists.