I gave away 200 copies of Darklandia and got about 15 Amazon reviews out of it. I would do another one if I didn't already have 41 reviews. I'll tell you all a little secret. The second I got 40 reviews on Darklandia, I got a healthy sales spike. It went away the next day, but I'm pretty sure that getting 40 reviews bumps you up onto one of Amazon's many secret lists.
I think doing multiple giveaway (at least 2-3 months apart) on the same book is totally fine. New people find LibraryThing every day. The ones who already won your book mostly likely won't enter again.
I've done two LT giveaways on Edge of Shadows (one in September and one in November) and gave away about 150 copies between the two. I picked up maybe 6 new reviews on Amazon, more on GR and LT (people seem to be more comfortable leaving reviews there than on Amazon). I know I've picked up some sales on the sequel as a result as well. I think it's a nice way to promote your work without putting in a ton of effort, and I'll absolutely do it again for that same title later in Q1 2013.
I found a lot of the same names were on subsequent giveaways for new books, so I've never done a second giveaway.
This is giving me a good idea, though. Perhaps after a year, I should do a new giveaway. I'll include a note that it isn't a new release.
I've found I get maybe 5 reviews for 100 copies out. They're certainly not guaranteed positive though, LOL, so if your ranking is good, I can see people not wanting to tempt fate.
The irony of book reviews is that once you're established, your fans will buy and review new releases, so you almost don't need the book bloggers/reviewers as much. It's like getting experience to get a job ... grrr hard to start cold!
I've done multiple giveaways for each of my titles. Like has been mentioned before, I've noticed there's a core group of about fifty that seem to request almost everything that comes around. But having repeat giveaways allows the more casual giveaway member to notice your book.
My review rate is really low though (1 in 40 or so). I've gotten a lot of three stars from the reviewers there.
Make sure and send the winners messages inside Library Thing, itself, explaining that you will be emailing them the file, if you email it, and asking them to put your email address in their directory. I did this, and I still had lots of them messaging me back, telling me they did not receive the email with the book. I think they expect the email to come from Library Thing...
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