You're forgetting something. A shared host is inadequate for a bunch of applications not just because of the number of visitors. It might also be that it's too restricted for you.
If you need to run some form of daemon for example, or some custom app in the background. Anything that requires more control over the environment, you won't find in a shared host.
I use and like both the linode and slice host libraries.
I already have a shared host for my crappy little blog, so I was just going to develop this new thing in a restricted subdomain to see if I could get it to become what I want. I figured could create a minimum viable product there, maybe have a bit of a private beta to figure out if anyone wants to use the damn thing, then shove it on a VPS.
That said, I noticed after I made this post that both Slicehost and Linode are month-to-month no commitment type deals, so once the site/app (what qualifies to be called a "webapp" exactly anyway?) is sort of ready, I'll likely just throw $20 at the problem and start on the VPS and see where it goes.
If you need to run some form of daemon for example, or some custom app in the background. Anything that requires more control over the environment, you won't find in a shared host.
I use and like both the linode and slice host libraries.