As you may (or may not) be aware, I do a number of book reviews every month and post the reviews here, on Goodreads and on Librarything. I usually put the post up through Amazon as well.
Amazon have recently changed their rules on who can review (in fact they have changed it numerous times over the past couple of months, but it seems to have settled), At present, I am unable to post reviews on Amazon because I have not reached the annual $US50 spend on books. This may surprise some of you considering the number of books I read, but you need to remember that I receive half of the books for free (gifts, loans, supplied by publishers/organisations) and of the remaining books, I buy at least 50% as hard copies. This leaves only a quarter of the books I read in the ‘purchased e-book category’.
I expect to make the $US50 threshold before Christmas, and will go through and update any reviews down prior to this on Amazon.