We stopped supporting the Kindle guide mostly because ever since Amazon released the Kindle 3, we kept on getting more and more support e-mails from users that had trouble with the guide. Even though we've always used Amazon's own tools to generate the guide, many users mentioned problems deleting or indexing the guide.
We started the Kindle guide at a time where we had no real API or mobile website for Feedbooks. The situation is quite different now: we offer a complete API using the OPDS standard that any client could potentially integrate, and we have a full mobile website, capable of supporting almost all of the browsing and searching option that we offer on our full website.
Every day, 10k+ visitors use our mobile website, and 50k+ use our OPDS catalog.
With both of these alternatives available on multiple mobile platforms, and the various problems associated to the guide, we decided that it was time to move forward and spend our time and effort on other methods of acquisition rather than on the guide.
I don't know what technical problems Hadrien had (I'm still waiting to hear back from him). But I checked the MobileRead Download Guide and it still works just fine on K4PC. It also worked just find on my K3.
This is truly an unfortunate event. In the early years of owning a Kindle, free over the air ebook downloads was one of the beast features. It was the one thing that made the Kindle so much easier to use than any of its competitors.
image via fling93