Well, my personal experience as someone who is totally unknown to most readers outside my genre is that giving an eBook away for free for one month GREATLY increased sales of the print edition. I've only tried the experiment once, but I don't mean we saw a small bump in sales -- I mean we sold thousands of copies of the $19.99 hardcover we never expected to sell. I don't want to self promote too much since I'm not a frequent poster on this board, but the website for the freebie was
http://www.DownloadTheDarkness.com if you're interested and some of the info about what we tried is still posted there. It really was a lot of fun and the "risk" of giving the book away for free definitely paid off in terms of finding thousands of great new readers for my work...
Brian