So I love doing facebook author take overs, why? Does it sell a ton of books, well no, but what it does do is add to the exposure I already have. As my other self I recently took part in a huge take over, we're talking 20+ authors, almost a week worth of days, and even special graphics. I was stressing because it seemed that I couldn't keep up with the others and every time I turned around I felt like I had missed something. There were a ton of bloggers looking for the authors to interview, people who needed all my information (and since I'm a slacker, I don't have my media kit together....). It was crazy and I remember telling my husband, "gosh I hope this is going to be worth it." Out of all the take overs I've done, it's probably the one that helped most. I gave out prizes, had a great time, and met so many new people, readers and authors.
Not long after that take over, I did my release party and holy cow was I surprised. My attending number doubled from the last release party and more than half were names I didn't know. NEW people. What's better is those new people came from that last take over and this was the first true introduction to my series that they had gotten. Many of them one clicked the free book and others went a head and bought all three. It was fantastic and guess what, they spread the news too. It was great and then they followed me to an event that I only took over for an hour and hosted the two days.
So my opinion, yes they are worth it, but I think like all social media events it's something you need to keep up on. Constant exposure, also giveaways are cool, but be careful not to break the bank or give out so many ebooks that no one is going to want to actually buy the book or books. What was great, I had one person who really wanted a copy of Criminal Behavior and didn't win it...so what did she do? She went right out and bought it! Woohoo! Make sure you keep it fun, don't make it all about your books, talk to your readers and audience. They know you're an author, that's why they are there. Tell them a bit about yourself and your books, give them a link and then let them discover things from there.
So when it comes to your tools of marketing, add take overs to that list.