I've done both the LT and GR giveaways. What they're great for is increasing awareness of your book(s). What they're not so great for is getting reviews. I've seen about a 10% review rate on the books I've given away through those two programs. You can [gently] request reviews in the description of the giveaway, but you can't make it a condition.
Reviews would be greatly appreciated = acceptable
Readers are asked to write reviews in exchange for the free copy = not acceptable
Still, they do get people to look at the cover and possibly read the description before submitting their request for the free copy. Several hundred readers doing that is well-worth the cost of sending out a book, IMO.
I've done three GR giveaways: the first two were for a single copy. The third was for 5 copies. About 700 people requested one.
Last edited by kcmay; 01-18-2011 at 02:58 PM.