Are there any downsides, Gizmo?
Cost. A real solid provider is going to cost quite a bit. You may find some for a cheap price but almost guaranteed the service, response, etc will be poor. Unfortunately there are so many junk resellers out there that it is quite difficult to find a good provider for any type of service.
If you can afford a VPS that's great but then your business really has to pay for it as the cost out of pocket is too much to absorb (IMHO). VPS is good when you want or need more control of what actually runs and how it runs on your system too. If your site is so busy that a good shared host can't run it well then a basic VPS probably won't be able to handle it either and you'll need to get a more beefy configuration which will cost quite a bit more than the basic cost.
