Let me start by saying I'm still undecided. I've read over and over about authors who offer the first book in their series perma-free and have gained many readers who might not have ever taken a risk on their books at regular price. The free book offers the reader a very good sample of the writer's style and if the reader enjoys the book then they can go on to purchase additional books in the series or at least by the same author.
The down side. I just finished reading a free book, The Emperor's Edge, and really enjoyed it. It was a book that I never would have purchased because it just doesn't sound like something I would normally like to read. When it became a 2013 Goodreads Choice Awards Nominee it grabbed my attention and since it was free I gave it a try. I'm glad I had the opportunity to read it because like I said, it was good! What's bad is I don't know if I'll buy the next book in the series because I can't help but wonder which other free books are out there that I would enjoy reading.
I guess with my one example the perma-free was a good idea. I personally would not have purchased this book but since I was able to read the first in the series free and found out I liked it, I am at least considering purchasing future books in the series. If it hadn't been available for free I would have passed the series by completely.
Do you usually buy other books in a series after reading the first one free?