I think a person's idea of Internet celebrity will vary per person. We all have different interests. I think Cheapy would be a high "B"-level Internet celebrity. Someone on a podcast, like say, Weekend Confirmed or the Giant Bombcast will say something like "Oh, yeah, of course I know Cheapy D. I love that guy."
That's celebrity. Plus, how many people (in general) can say they've been featured in Forbes? Cheapy's fortunate enough to make a living off what he does on Internet. That's legit stuff.
Anyhow, regarding other people who became celebrities solely based on Internet presence, I think YouTube celebrities (e.g., that Ray William Johnson guy, Kassem G, etc.) would be "A" list. Those people have leveraged their fame into TV commercials, TV shows, and legitimate career opportunities.
Just my two cents. (This isn't a contest entry, by the way.)
P.S. UFC 143 is today. Diaz-Condit has Fight of the Year potential. Here's the CAG MMA thread