I wonder if people start abusing this if Github were to put any restrictions on it somehow. For quick one off single page things sure why not, but if people start trying to host huge websites on Github? I'd be curious as to their response.
Unrelated to porn this sort of thing could be great in general as all the content is searchable it would be a goldmine for information on how to use a function or do some specific action. I already use git as a codex of sorts!
and
If your bandwidth usage significantly exceeds the average bandwidth usage (as determined solely by GitHub) of other GitHub customers, we reserve the right to immediately disable your account or throttle your file hosting until you can reduce your bandwidth consumption.
I wouldn't worry too much about it.
They'll have to restrict it to some extent, but neither is it 1995 anymore. GeoCities was able to make a go of 15MB per free website (with bandwidth caps) for 14 years (1995-2009), and it's still available in Japan, but I don't know the current terms.
Serving static content you don't pay for from storage you already own down pipes you already pay for is just about the cheapest way there is to be online by any metric. I wouldn't be surprised if they could support a fairly large number of websites without blinking.