As pointed by countless people before me -- the hard part is not necessarily the hosting itself (which is still hard and could be a problem at a certain point),

As pointed by countless people before me -- the hard part is not necessarily the hosting itself (which is still hard and could be a problem at a certain point), but to moderate -- to filter out spams, insults and illegal stuff etc. That is a time black hole. You have to admit that reddit does a much better job at fending off spams than an average forum.