I posted a reply to Guido his blog. What I suggest is that initially you may benefit, like he says.from focusing your marketing efforts to get a sales spike at the big sites. But once it becomes obvious that, after price changes and many promotions, your book will not sell as before, it may then make sense to place it in other outlets. One possible other outlet to place e-books is Scribd.com. They have millions of readers although their sales/marketing infrastructure for authors is not as advanced as in other sites.