When is it time to get dedicated hosting? Anyone been through this?

[ferrazf]

Hi,

I am currently running a site where most my traffic is at the forums. I wanted to know from you guys what kind of (active)  member numbers or any other statistic to look for before thinking about upgrading.
I don't have any mods installed, except for a custom theme, Amber by TP's Bloc.

I know the appropriate time to switch would be when you experience slowdowns, but there must be a general bottleneck statistic relating SMF + activity + shared hosting. When did you decide it was time to switch?

Thanks!