said by intok:300Mbps was an optimistic figure considering only the first two aggregation layers.
What BosstonesOwn said as well as 300Mbps during peak time kicks the everloving crap out of your best case scenario on everything but the fastest muni or google FTTH installs.
If you look at other high-speed low-cost providers like HKBN's 1Gbps for ~$35/month, peak-hour speeds to sites/services outside HKBN's own network drop to 30-70Mbps... and even within their own network, speeds do not seem to exceed 300Mbps very often. Of course, still beats the pants off anything we can get for $35/month here.
As for Google Fiber, there aren't enough people on it to draw conclusions yet but my hunch is it will turn out somewhat like HKBN if they roll it out to enough people for it to make a dent in Google's existing bandwidth pool.