I pre-ordered the latest Redwall novel, The Sable Quean, from Amazon several months ago. At the time, I was quoted a price of $16.19, well below the MSRP of $23.99. The book arrived yesterday and today I got an e-mail that they only charged me $12.95, the lowest price since I placed the order. Out of curiosity, I checked Amazon's web site and they're currently listing the book for $14.03, so by pre-ordering, I saved an extra $1.08!
If you want to order something from Amazon but it's not out yet, go ahead and pre-order. You might just save some money.