Anything that is better than the Sony would be good. I never meant to read PDFs on the thing, but I've found I actually do quite a bit and currently it's a right pain.

The Sony organises books into "Collections" - I'm guessing much like the Kobo shelves. If I tag a book, say, "toread" in Calibre then it automatically appears in a "toread" collection on the Sony when copied across, which is very handy. It looks like you can get the same thing to work with Kobo shelves, although it takes a bit of fiddling.