Well, in my experience anything dedicated with scsi should be decent.
Iíve seen many forums grow on shared servers like ipower/hostgator and they reach their limitations quickly!
Most the time they will penalize you if you have more than 100 sql connections under your account. So if you have 4 web forums and they all have 25 users on it, they shut it down. Some places are known to suspend for up to 24 hours, talk about a way of telling your members not to return
Shared dedicated really, to me still just seems like a shared $9 box, but make no mistake, it is an upgrade in a company that is not over selling their boxes.
I went through a phase where I had called ipower at least twice a day because cpanel was crashing their sql. They couldnít figure it out. Its sad when you know all the level 1 through to level 3 techs and team leaders. They used every excuse from shifty coding on my part to shifty coding on vbulletins part. At no point did any of the techs take control, or accountability of the problem. The team leader was very nice and reassured me that the issues would be resolved, that made me feel better. But ipower does have many horror storiesÖ.
Unless youíre running a huge forum, reselling or running multiple decent sized boards, I donít see the benefit of a dedicated server.