How do you define success?
In general, though, I would go with a lower bar than fallentimes's suggestion. How about any company that is now incorporated and could be seen on a path to being something that someone would want to acquire, i.e. has any of these properties: is actively hiring, has raised money, is generating profits, and/or has a significant (>20K?) and growing user base?
Both Skribit and Twitpay are incorporated.
Skribit will hire its first full time person in January upon closing a small round. The company has significant user traction: http://siteanalytics.compete.com/skribit.com/?metric=uv
Recurring profits/issue dividends/get acquired
Unless someone has better metrics; success is hard to define.
Profits, in general, take years and may not be the best way to define success for startups (at least young ones). Profits should be the goal however.
Getting acquired is a good measure but this too, typically, takes years.
Issuing dividends...is just too far into the future for most startups.