I have published a few collection Kindle eBooks, and am planning on publishing at least 3 more in the not-too-distant future. While my experience with the Kindle marketplace has been mostly positive, I have been wondering about the other options out there (such as Nook, Lulu, Google Books).
Has anyone published using multiple platforms and seen a decent amount of increase in their sales to warrant the (admittedly small) amount of effort it would take to publish to those other marketplaces?
Would an independent writer be better off locking in to only the Kindle marketplace, given the tools available to the writer through Amazon?