&gt; Not anyone can grow it to a userbase of hundreds of millions of users.<p>Yep.<p>&gt; Scaling wasn&#x27;t an issue; once you have investment and users, you just throw money at the problem.<p>Yeah not really. The CAP theorem is going to bite you if you just buy more servers. Twitter suffered huge growing pains as it tried to scale after becoming mainstream--remember the &quot;fail whale?&quot; Facebook completely re-engineered PHP to address performance and scale issues.