Hi This is a bit late for an answer but I've just taken possession of a new MBP and was browsing the forums as I have a few issues too. On this topic my thumbnails werre all blank to start with but as I have used the sites they have slowly returmed until now they are fine. My issue is with Preview. I used to be able to combine PDFs after scanning but now? I'll need to post this question elsewhere methinks.
Hope things work out for you