Yes, there are plenty of companies out there that very much depend on a network effect and aren't Y Combinator-funded: Digg, Facebook, Quora or Stack Overflow, to name a few.
Additionally, 3 of the 4 had major PR behind them. Kevin Rose was on ZDTV/TechTV where he publicly talked about (and where I first heard about) Digg; the Quora guys got famous as the "ex-FB executives" who left to form their company; and Stack Overflow was huge because Joel is one of the most famous programmer-bloggers in the world.
The first, prototypical YC TechCrunch launch article doesn't always tell the whole story behind a company's history and founding (in our case there wouldn't be room ;).
Probably not. I'm currently bootstrapping a search sharing network at Seekier.com and it's extremely tough to gain any sort of traction without any previous exposure or network, which unfortunately results in me making replies such as this. The only alternative is to implement Facebook, Twitter, and/or Google Connect integration to help spread the word organically through those networks.
I think you are absolutely right...it will be extremely tough to gain instant traction without a previous network. However, as fast as the tech world moves, I think taking a bit of an old world approach can really pay off. Take a step back and think about forging real friendships and loyalties, and letting it happen slowly. You can build a lot of social capital by just doing favors for other people...but obviously try not to be Don Vito Corleone "Some day, and that day may never come, I will call upon you to do a service for me, and you won't refuse"
So, I want to encourage you to start building that network now that will become your 'previous exposure or network' by fostering genuine relationships with people you want to meet and even your current competition.
