This just in:
5 days after it was released, To Sleep In A Sea of Stars is now ranked...
#284,586 in Books (Paperback version)
#87,730 in Kindle Store (ebook version)
#39 in Audiobooks (audiobook version)
#339 in Books (hardcover version)
#1,062 in Books on CD (Audio CD version)
So, the audiobook is relatively popular, at least among audiobooks being purchased on Amazon. But the rest of those numbers? Damn. This soon after release, these sorts of rankings are almost inconceivable. The Brisingr paperback is an order of magnitude more popular at #28,498 in Books (paperback), and that was published in 2008!
For comparison, Dune (published in the 60s!) is currently at number 39 in Books. (edit: It has come to my attention that Dune is currently bestselling again because there is a new Dune-based TV series either planned or showing on one of the various streaming services).
The Publication Manual of the American Psychological Association is at number 95.
I think it's fair to say the launch of To Sleep was a bit of a flop. Let's see if it increases in popularity over the next few months.
edit: a few hours later, the paperback has jumped up to #69,581 in Books, and the audiobook is number 6 in Science Fiction (audible audiobooks). The Kindle ebook has jumped to #57,053 in Kindle Store.
I think the audiobook might be so much more popular both because of Jennifer Hale, and because it is currently free to Audible subscribers. Compared to $15 for the ebook and $26 for the paperback. That second point probably makes a difference.