This article is the first in a series for community owners who have outgrown a VPS or a larger shared hosting environment, and need their own server to handle similar load levels without running into bottlenecks, but want advice about what they need, from someone who has been there. Since both of my major communities are adult, I created this site in part to serve as a decidedly non-adult repository for presenting what I have learned.
For my own experience, I run two of the most active communities on the Internet - Elliquiy Adult Roleplaying Forums and the Blue Moon Sexual Role Playing Forum. The splash page of each forum does not involve anything racy, but the images and text inside of said forums might not be so gentle on the pure of mind - be forewarned.
As you take up more and more of your host's resources on a machine - whether high-end VPS or high-end shared - you are going to consume more and more of its I/O bandwidth. On a good host, this will typically be higher than what your first dedicated server would be - however, you are at the mercy of everyone else on the machine. And you will notice, repeatedly. When you or your host get fed up with this, it's time to move to a dedicated machine.