I have a share hosting, and I charge 150$/years to host company website. Those websites have a maximum of 2000 person per month accessing the site, mostly WordPress site. So everything is fine until a person in Facebook, with 300 000 friend talk about the website. You know, if just 10% go see the site, it's 30 000 person at the same time accessing the site, and what should append just append, the site crash, and then after 1 hours, it's back on...
So the question, how to cope with that kind of load ?