A year and a half ago I had a long-dormant Goodreads account. I'd never tried LibraryThing or Shelfari. But with the contract in hand for my debut novel, ASHFALL, I knew I wanted to get more involved in these excellent social media sites for readers. So I revived my Goodreads account and joined LibraryThing and Shelfari. I set up profiles on all three sites and made sure the metadata for my book was correct.
I had a much harder time connecting with people on LibraryThing and Shelfari than on Goodreads. I quickly amassed more than a thousand friends on Goodreads (now, on 2/3/12, I have 2,800), but couldn't make any similar inroads on the other two services. A discussion of post-apocalyptic books on one of Goodreads' forums led to a connection with a couple of Barnes & Noble staffers who've become some of ASHFALL's staunchest supporters.
When the ASHFALL ARCs were released, I decided to try an experiment. I offered a signed ARC as a giveaway on both Goodreads and LibraryThing. (As far as I can tell, there's no giveaway feature on Shelfari.) I used the same description and giveaway time period for both, to make the comparison as valid as possible. The result? 1,357 people requested the Goodreads giveaway; only 188 requested it on LibraryThing. Since then, I've offered giveaways only through Goodreads--they routinely get between 2,000 and 2,500 requests per month.
My conclusion is that Goodreads has won the battle of the readers' social media sites. I recommend that new authors set up a profile on LibraryThing and Shelfari and make sure the data on their books is complete, but other than that you can safely ignore both LibraryThing and Shelfari. I plan to run another giveaway this month on both Goodreads and LibraryThing to retest this conclusion--if I learn anything new, I'll let you know.
The one big drawback to Goodreads? It's buggy and frequently down. I wanted to test targeted advertising on Goodreads, but I can't get it to work. I have some worries about the survival of a site that can't even figure out how to take my money. My guess is that advertising books on Goodreads will be just as ineffective as advertising them on Facebook.
What does work on Goodreads? Giveaways. I can get 2,500 people to click 'I Want It' and read a short description of my book for the price of one hardback plus shipping? Sign me up!
Don't do it the way the big publishers do, though. They throw 30 copies up at once and then never repeat their giveaways. Do lots of short giveaways of one copy. I do one every month. Why? Advertising is all about getting people to engage with your message over and over again, until it sinks in. If you do a giveaway every month, they see your message every month. You'll get a far bigger bang for your buck doing ten one-month giveaways than doing one ten-copy giveaway.
The "rules" for interactions on Goodreads are the same as for all social media:
1) Treat others the way you want to be treated.
2) Don't feed the trolls (ignore anyone who tries to bait you.)
3) The only appropriate response to a review, even a bad one, is thank you. (Even a harassing or personally abusive review should not be responded to. Instead, report it to Goodreads. And yes, sadly, this happens occasionally.)
Hope that helps. If you want to know anything else about readers' social media sites, comment and I'll edit this post or add another. Thanks!
EDIT: There's a much more thorough post by Caleb Ross here that comes to the same conclusion--Goodreads giveaways work.
Edit #2: Now that Amazon has bought Goodreads, I no longer believe it's a good choice for authors. We need diversity in our retailers and book recommendation sites. I now use BookLikes.