I was referencing the OP's comment noting the few Startup Weekend projects that have been successful. Which projects are among these few?

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?

I can only speak for those I know.

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

For the purpose of this conversation, let's define it as one or more of the following:

Recurring profits/issue dividends/get acquired

Unless someone has better metrics; success is hard to define.

I think for a startup weekend type event you have to define success as any company that follows through after the weekend and gets a non trivial amount of users.

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.

Oh ok - I didn't really know how long startup weekends have been going for. So now we have to define what a non-trivial amount of users/traffic is :).

Probably the most important thing is growth.

If those are the metrics the answer is zero Startup Weekend companies are successful. I would say it is too soon to tell for many. Somewhat like a YC company at the end of a session.

Another thing to think about is the main goal of Startup Weekend is not to create companies, but to build community.

Good point. And it seems like it's been very successful at doing that. It'd just be awesome if one (or more) of the startups made it big.