when to upgrade to vps

I mean, you can get an 80 dollar package with at least one company and who wouldn't want the speed? Note, speed means a lot in the user experience and who wouldn't want the best? Finally, what do you all think would be other good reasons to use a server rather than a VPS or shared package?

When is the best time to order and upgrade to a VPS? With many hosting companies offering 'unlimited' or 'unmetered' disk space and bandwidth, when would be a good time to upgrade? If you have everything you need on a shared hosting plan and they give you 'unlimited' resources as they say, would...