For a friends birthday recently I made a notebook, but tried including embroidery on the front and back cover. I did a simple floral design with her initials in the middle onto dark green cotton, which I used as the cover instead of patterned paper. It worked quite well and she liked it, but I realised it is more difficult to stick down and it wont lie flat because of the differing height where the stitches are.
I then tried again with a different size book, A5 instead of A6, I did a lion design n the front and the Lannister motto from Game of Thrones on the back "Hear me Roar". The embroidery looked great but once again the difficulty was it lying flat and me effectively sticking it down. I tried using PVA glue but this wrinkled the card I was backing it onto, so tired again with hot glue as I'd used on my friends, but again this made it unsmooth where the glue was underneath. I ended up using glue stick and double sided tape and this seemed to work better. I also put thick interfacing behind the embroidery to try and get it lying flatter. I haven't yet added the pages but plan to.
I might try a cut out with the embroidery in on the next one, like cross stitch greeting cards, this way I can still include embroidery but have the stability of a paper cover not a cotton one.