While Amazon continues to withhold demographic information about buyers from KDP authors, Kobo’s Writing Life platform has gone the other way: apparently Kobo Writing Life’s sales reports – the first of which are going out at the moment – list the zip code / postcode (delete as applicable) of buyers!
I haven’t been able to confirm the claim myself, but (if it’s true) it’s quite a big chunk of information. In the US, zip codes can cover fairly large areas, but in the UK they usually represent a single street. There are no privacy problems here as far as I can see, since the information doesn’t allow an author to identify a particular individual, but it does allow authors to get a really clear idea of where their buyers are located.
While some authors might obsess over the data, there’s not a huge amount to be gleaned from studying the postcods and zip codes. Nevertheless, if you find that your Kobo sales are mainly coming from one particular area, it could tell you something about how your books are appealing to certain demographic and psychographic groups.