On one end, there are the companies that fail; for every dollar put in, exactly $0 came out in the end.
The other ("success") end is more difficult to define because there is no end point; the company that is furtherest along that end of the spectrum might not hold that position forever if an even more successful company comes along.
I think the natural tipping point between failure and success is the break-even point, perhaps adjusted for inflation. A company that does just a bit better than breaking even for investors isn't going to overwhelm anyone, but it's the point at which most people won't feel too bad about having invested in the company. Top investors who are used to yielding massive gains will perhaps not feel the same way about that, though.
The more interesting part of his question was the objective criteria for determining success, not opaque opinions about one example that fits into the gray area.
Loopt apparently sold for $43m, but had $32m investment. I don't know if that's classed as 'success' or not.