There are quite a few things that can slow your connection down besides connecting via WiFi. Your computer's network interface card (NIC) also makes a difference. Fast Ethernet (or 10baseTx) cards can connect at only 100 Mbps, whereas Gigabit Ethernet (or GigE or 1000BASE-T) cards are necessary for connecting at 1 Gbps. Some newer laptops, especially some netbooks, do not come with Ethernet cards or connectors, but you might be able to connect a Gigabit Ethernet adapter via the USB port. To get gigabit speeds, it needs to be connected to a USB3 port. The Ethernet cable itself also matters. Cat5e cable can transmit at 1 Gbps and Cat6 can transmit at 10 Gbps, but Cat5 can only do 100 Mbps.
Other things that can affect your download and upload speed are the age of your computer or device and its hardware, the connecting device's configuration, the operating system, the web browser you're using, whether you have other applications running and whether another device that plays video (including your Google TV box) is running or even just connected and turned on. Video (including Google Fiber TV) takes priority over data, and data gets to use whatever bandwidth is left over. All devices on your home network will also be sharing the bandwidth, so having multiple devices running might slow down your connection a bit, especially if any of them are streaming video.
Some websites (and areas on the network between your computer and the sites you're trying to visit) won't be running at 1 Gbps, which will affect the speed at which you're able to upload and download data. Any network congestion occurring anywhere between you and your desired data will also slow you down. Some sites simply cannot serve out data as fast as Google Fiber can consume it. Netflix's servers, for instance, can only process streaming HD video at 5 Mbps [source: Talbot]. Google is working with major content providers, including Netflix, to allow them to connect directly to Google's network, and in some cases they're even letting those providers put their servers directly in Google's Fiber facilities (co-locating) to make transfer of content to users even faster.
Google doesn't impose a data cap or throttle users' speeds for how much they use like some providers do, but the company does state that it might slow down users' connections during times of extreme network congestion in a manner equitable to users.
Even with all the possible things that might slow down your Google Fiber gigabit service speed, it should still be far faster than most of its broadband competitors. Google also offers a slower 5 Mbps download and 1 Mbps upload service, which is comparable to the basic broadband offerings of cable and phone providers.