When to switch from Shared Hosting to VPS Hosting?

The question of when should somebody switch from a Shared Hosting account to a Virtual Private Server (VPS) is one that is asked time and time again.
Virtual private servers are the ideal choice for many who require more than what a shared hosting account has to offer, but do not have the budget for a dedicated server.
If you are one of these customers, then this stepping stone solution is ideal for you.