Overall it's looking really well thought out and layed out. I think the main focus would be to work on hierarchy a bit more. Some feedback for you:
Home Page:
What happens when you click on "Add to shelf" does something drop down? I would expect something to dropdown since it has an arrow, but I'm not sure what this interaction would be. It might be worth designing this out.
Under the reading challenge the "books this year" is not aligned with the input box
Where is the search box on the small version? Also, why does the search box have a gradient that makes it look like a button/is different than all of the other inputs on the page?
The "start challenge" button seems to need more padding on top and bottom and maybe a more subtle/concentrated gradient
The sponsored books in the large version should either have 3 options to span the page, or should be stacked on top of each other in the sidebar. Right now it looks a bit strange because there is a lot of extra space on the right side.
the tabbed section should take up more space on the page (2/3rds maybe) instead of 1/2 because it is the most important information.
Profile Page:
There should be more differentiation between text in the text next to the profile image (bold/larger/smaller/lighter color could help to differentiate info more).
The subtle drop shadow works really well on this page
There is a lot of orange text around the comment box that makes it all look clickable (like links). Make sure the items that are just text don't look clickable and maybe make some of those look like buttons instead of just links (similar to the load more updates button on the homepage)
The ad should be left aligned to the heading text because it isn't "inside" or "underneath" one of the headings
put the ad underneath the comments section (it is the least important thing on the page, although it would be a good a/b test to run)
My Books Page:
The sorting options for the books should be at the top of the page. What if you have it sorted by "view all" books, then you would have to scroll through a lot of books to adjust the sorting options
adjust the hover/click overlay so that it relates more to the book it is describing
Select inputs could use more top/bottom padding
really good hierarchy on this page
I'm reading the sorting options as " Items per page, 20, ascending" (the ascending and descending look like they are related to the row instead of the column). Maybe add a label for those as well or add the "sort by" into it's own column
Overall it's looking really well thought out and layed out. I think the main focus would be to work on hierarchy a bit more. Some feedback for you:
Home Page:
Profile Page:
My Books Page: