GigaOm reporter Dave Greenbaum recently visited Mud Pie, a vegan cafe in Kansas City that has secretly had Google Fiber running for several months. Greenbaum performed a few speed tests and found that, as expected, speeds were affected by the limitations of the 802.11n Wi-Fi specification, which struggles to reach over 160Mbps. Even over ethernet the reporter couldn't download at anything like the advertised 1Gbps speed. He also mentions that HD video playback became "glitchy" when another cafe user started streaming a movie. The report theorizes that if you were to record the maximum eight shows at once using Google's Fiber TV service then your internet would slow down. While it's not impossible that the Fiber TV service and internet connection share bandwidth, it's unlikely that streaming eight channels would take up much more than 20 percent of your 1Gbps allowance.
It's worth noting that Greenbaum's tests as a whole were anything but scientific. The reporter shared the connection in a public cafe and downloaded files from notoriously slow sources such as apple.com, which struggles to keep up with our current 50Mbps home broadband connections. Although third-parties aren't ready to deliver anything close the speeds that Google Fiber can offer in a straight http download, it doesn't appear as though there's too much room for complaint.