Going to Fred Meyer (a "superstore" not unlike Wal-Mart, but better, and the electronics source of choice for many in the American Northwest), all the (wired) routers have gigabit Ethernet switches built in, and all the standalone switches themselves are gigabit. It's been many years since you could buy a computer that had mere "Fast Ethernet".
Which is to say I think it's at least somewhat common for a household -- even a non-geek one -- to have gigabit.
Which is to say I think it's at least somewhat common for a household -- even a non-geek one -- to have gigabit.