Strange, I had an update to the PC software here today and I fully noticed I could arrange collections I wonder if the EU has different software to the US Kindles? There is a 99.9% chance that I did not notice this feature.
I didn't notice this collections feature before. My Kindle account is *ahem* in LA so I can buy stuff from Amazon.com. But I use the iPad Kindle app 99.9999% of the time and tend to archive stuff I've read. Just checked, no categories in the app.