This depends on the size of your traffic. For example if you have a single site that is 100kb in size than you can serve a lot of people, maybe 50 000 per day.
around 10,000 and above visits per day but VPS might still be a good option before you move on to dedicated hosting.
only when you hit 10,000 hits a day
hope this helps - http://host4dummies.com/introduction-to-...
In thousands of people?
