Me personally, Twitter does next to nothing for me insofar as traffic to my work goes. I should say that I do not use Twitter. If I were to spend lots of time promoting my stuff, I'd be getting less stuff written. So I only use one social network, and that would be Facebook.
I get lots of views from Facebook. Seriously - lots. But I work hard at putting the right links in the right places, and not looking like or being a spam person.
I don't know for sure, but I sure do imagine that were I to have chose Twitter to be my social network instead of Facebook, that I could get lots of views from Twitter. I just don't like Twitter. The whole 140 characters, or whatever the number is - I have more to say than that.