I emailed PictoBooks about this issue but haven't heard back yet, probably because of the holiday weekend.
I know they want you to design pagespread layouts with 1/16 extra on the margins, but what about the center of the pagespread - the part that will be sewn into the spine? How much "clearance" do I give there? I know PictoBooks has a "split spine" binding feature that makes each image lie totally flat and gives a "seamless" flow to photos that take up both sides of a page spread, but unfortunately I cannot find info on how to design for that on their web site. They have a design tool, but it's offline right now due to some kind of funky errors it was having in November.
So, if anybody's used PictoBooks before, can you please enlighten me?