Well I got 18869 visits across all my sites in March - an increase of 8.2% on Feb, so not bad.
Almost all my search engine visits were to my authority blogs (and most of the income came from them too). Authority blogging takes a lot of time, especially if you are doing it all by yourself, with no spinning or outsourcing, plus a good quantity of research is thrown in, to make the posts valuable. But it definitely starts to pay off once you have some volume, and if you have been paying attention to your internal linking. You don't actually need many external links if you are careful about internal linking, really good content, and building a volume of content (one tip: turn your feed off on the authority blog - unless you are in a social niche, you don't need it, and feeds are just an invitation to spammers to scrape you). I'm starting to think that how frequently you update plays a big part in Google's trust, along with the mass of content.
So I am going to continue with the above, and perhaps start one more authority blog if I have time.
My Facebook experiment is inconclusive so far. The first page I tried it on was for a narrowish keyword, and within two weeks, it was sitting on page 1 of Google, and is holding the rank. The second site I tried it on hasn't been so fortunate, but it's a more competitive keyword. I need at least ten examples to be able to say conclusively whether facebook helps or not, so I will try to do some more this month.