Traffic Volume Limit?
 

Is there an upper limit for how much traffic a VBulletin forum can handle? For example could it handle three million hits per month?

There is no real software imposed limit. But beyond 5/6 million pageviews per month you may require multiple boxes to keep stuff running smoothly.

Are you kidding? I'm on shared hosting and I'm averaging roughly 3 million hits per month (less than half being from googlebots) and my account barely breaks a sweat, I never see server load past 4 percent. I also run a wordpress blog on the same account, same domain.

A hit isn't a pageview... there can be hundreds of hits per pageview.