My girlfriend started DEVOURING a freebie I picked up from Amazon months ago. I gave her a ipod touch so she could use my books and she just stumbled upon it. I've never seen her read like that! And she'd never have ran across it without the freebie. There was one more by her that was given away, but I'm sure all of them will be purchased now.
It was
In the Bleak Midwinter by Julia Spenser-Fleming. It's "Female Episcopal Priest Detective" It's filled with lots of Episcopal inside jokes and as both of us are going to be priests in the church, it tickles her a lot. Evidently it's a good book, too.
I don't mind buying books. But since I've had an ebook reader, freebies have definitely done good for the authors doing them that have existing bodies of work. They didn't lose a sale because I never would have bought them, but gained purchases they wouldn't have for their other books.