There's no doubt in my mind that social interaction plays a huge role in just about every aspect of life. And I don't mean things like Facebook or any other virtual community but real, personal face to face contact.

In my experience it's a lot like Dagny said. The best jobs are never advertised or are impossible to get for an outsider without any personal connections. I've been privileged enough to get a very attractive position at the very start of my career, which is especially significant given that my profession is highly specialized and finding a decent job is extremely hard for a person fresh out of the university with no prior experience. Much of it had to do with the fact that I studied hard and accomplished a fair bit in my time. But if it weren't for some personal intervention and recommendations from people way higher up the food chain there is no way I'd ever get a decent chance to do what I'm doing now.

I'm not saying you should promote yourself loudly at every opportunity. I happen to be a fairly modest person myself. But if you want to succeed at just about anything in life you need to get in touch with people who share your interests or are involved in the same line of work. If you're good at what you do this interaction will help your career and reputation enormously.