The thing is, from what I can see, there's a 'New, Old Boys Club' and it's twitter. These old fashioned clubs were basically a way of getting to know the people who mattered, getting an in with the important people. And twitter can do that for you.
I was going to write a really long post about all the ways twitter can help you in the way 'Old Boys Clubs' could, but it was REALLY LONG! So here are just a couple and I might elaborate in the future.
#1 - Talking to people at the top of your field
One of the great things about twitter is that you can send a tweet to pretty much anyone and if they reply, hurrah!, and if they ignore you, no harm done, and if they think you're an idiot they probably won't remember who you are in the real world anyway.
All of this makes it much easier to get a dialogue going with 'important' people, the kind of people you probably wouldn't approach at a conference unless they were old buddies with you supervisor (i.e. Old Boys). And if you did approach them at a conference and found you had nothing to say, or only things they thought were stupid etc., that could be pretty embarrassing. But twitter removes that for you. So go and tweet the scary people, you never know who'll find you really interesting!
#2 - Job Adverts
My contract is coming to an end, so I've been looking for jobs. I check jobs.ac.uk everyday. But the 2 most interesting job adverts came from twitter.
The first one, I sent out a tweet saying "Anyone know of any postdoc jobs going in Bioinf or comp genetics?". And someone replied and I got an interview, I didn't get the job, but you can't win them all. Another job was posted on twitter recently, one I didn't find on the job websites, and I've applied and I've got an interview. Fingers crossed this time.
So although I check all the websites regularly, the really good jobs came from twitter, jobs you wouldn't necessarily find otherwise, because this is the insiders network.