It all boils down to load balancing the servers often. A server running 100 websites with no problems can change 2 months later when a few sites start getting really popular and drawing more resources. If a host does not monitor these things, they will surely run into trouble. We just run dual xeons and you can pack quite a few accounts on them but I refuse to do it. I am not that money hungry and I also want to keep my clients happy.
