As you can tell from the sparsity of my posting on this blog and my lack of facebook / twitter / etc, I am not a very social-media person. It did not thrill my little heart when a coworker came up to me the morning after a Company Event, and said "I saw the pictures of you all over mytwitbook!" Nor did I rush to pull out a smartphone and retweet or "like" everything. (Those of you who like me anyway, thank you. I like you too, as friends and acquaintances, not as clicky-button-instead-of-adding-coherent-commentary.) I feel it's important that you know my stance, so you can vary your "take with grain of salt" dosage accordingly.
So, how important is social media? Do you have to participate? How many accounts do you need to have? How often do you have to tweet? Cart. Horse. Wrong questions. Try this one instead.
What can you gain from using social media, and what return on investment can you gain from time spent? How do you maximize this?
The single most expensive thing you can spend is your time, because you don't get it back, and there's no way to get more. It's also the thing that every one of us gets (until we don't), and therefore the easiest to spend. Tomorrow you'll have 24 more hours to spend that day (G-d willing), no matter what the state of your bank account. Some are sunk costs already: if you don't spend at least 6 sleeping (8 for me) and at least 1 eating, the rest will be pretty miserable. Of the remaining, not all are equal for creative work. May writers do best in the morning; others do best in the late evening, and some will have to make do with whatever can be squeezed into while the baby's sleeping, waiting for customers to check in or between patients.
Many writers transitioning to full-time are startled to find that they don't have 8-10 hours of writing in them; the brain is a muscle, and after 2-5 hours, it goes to mush and won't put out any more creative work. (It gets better as you train it, but there is a practical limit.) This leads to indie authors writing in the morning and editing/marketing/business matters in the afternoon, as they don't require the same skill sets. Keep this in mind, and schedule wisely.
Now, to the meat of the question: what is the point of a blog/ mytwitface account?
1. Gain reader exposure / attract readers
2. Retain readers' interest, building name recognition.
3. Build excitement for the next release, so you can
4. Spike your sales in the first few days of your book release / sale
No, interacting with your readers isn't a goal, it's a process. It's how you accomplish your goals.
Goals 1-3 are very fuzzy and hard to measure. "Raising awareness" is so nebulous entire charities make their mint and pay their execs handsome salaries on doing just that while never having to provide any actual outcomes to justify their existence. As indie authors, though, we'd better find ways to quantify and qualify to see if we're wasting time that would be better spent writing. You measure these by site visits and click-throughs, "likes", retweets, etc. Keep in mind, though, the sad fate of a nearly unknown writer (not even sure she was published yet?) telling Larry Correia that she was better than him because she had more facebook friends... don't get obsessed with these metrics, because ultimately, they only matter when you translate them to the action on goal #4.
Strange as this will sound to you, the five years of daily blogs that Calmer Half put out before he released the first book only made a difference for three days. The same is true of mailing lists - you may have 18,000 subscribers, but it'll only make a difference for 18 hours. The point is: your audience on your soial media, whatever form it takes, is not the main audience that will buy your books - the main audience is a vast unknown mass of readers idly browsing amazon, looking for something to read. Your social media audience is there to help you spike the sales numbers on release, drawing enough sales fast enough to kindle (heh) that fire. Once your fans put you on the bestseller lists, and tell people about you, then the world will be able to see and buy your book.
So first, you want to get them excited about an upcoming book. You'll be excited about it, and share that enthusiasm - the joy of finishing the draft, the excitement of the cover reveal (sometimes authors even do two or three options, and kick it out to their readers to help decide which is the best cover. This engages your audience, making them feel excited and invested in the upcoming release.) Some authors release snippets, teasing the audience and whetting their appetite for the rest of the story.
Second, DON'T SPAM YOUR READERS. Did I make that clear enough? Look, Calmer Half gets about 3,000 visits/day. The sell-through rate (people who click on the release announcement to go buy) is much lower than that, and it drops by 50% every day after release.
So, if 100 people click through and buy the book on release day, 50 will on day 2, then 25 on day 3, 12 on day 4, and 6 on day 5. This happens whether we mention the book every day or not; it's been a consistent pattern across all releases. By Day 5, the sell-though rate from "buy my book!" is indistinguishable from background sales through the pictures on the sidebar, by infrequent readers just noticing or browsers who just found the blog being curious enough to click through and check out the books. So by Day 5, announcing again won't help sales, and will annoy the people who've already bought the book - or won't get around to it for weeks.
Third, What do you write about inbetween book announcements? Something that interests you (they won't be excited if you're not excited), and will interest your target market. Which means, don't write primarily about writing. The only people who want to talk about whether or not it's okay to have first person protagonists are other writers, not readers. (This isn't to say never do it; people are fascinated by how things are made / done behind the scenes. See the astounding popularity of Dirty Jobs, How It's Made, Deadliest Catch, etc.)
For blog examples, which tend to be longer format than mytwitface, My Calmer Half has everything from articles on airplanes to cute Peruvian commercial. Sarah Hoyt has social, political, and feline commentary. And free novel chapters. Cedar Sanderson has book reviews, food photography, life updates, snippets of upcoming books, and art. Dave Freer has the "mundane" (only to him and his neighbors) everyday adventures of homesteading in Flinders Island, Tasmania. Larry Correia has a serial adventure written from his gaming campaign, pictures of minis (miniature models for fantasy armies) he's painted, social commentary, book promotion for friends and good causes, and fisking trolls.
For shorter form, see Larry, Sarah, Marko Kloos, or high-selling authors in your genre on facebook - and for very short format, see them on twitter. If you're better at coming up with snarky bumper stickers than articles as long as this, you're probably going to be better showcased on twitter. If your response is "any philosophy that can fit on a bumper sticker is idiotic", you'll probably do much better on blog.
Be warned: Facebook has a habit of censoring how many people can see a post with a link. So if you send "my book's out!" with a link, only 180 out of 3000 people may see it. The current workaround it to post the announcement sans link, and add the link in first comment.
More on click-through, sell-through, and advertising another day.