Club Nintendo was discontinued in PAL regions on 30th September, meaning that fans around the world are now simply awaiting news of its successor. Bizarrely, though, the actual catalogue is still active in Europe, and if you have leftover stars you should be able to get some downloadable treats.
When you browse for Club Nintendo on the official site you get a message confirming it's discontinued along with a sign-up box for future updates, yet if you go directly to http://stars.nintendo-europe.com/, you can still browse and 'purchase' goods with leftover stars.
We suspect that ordering physical rewards will end up with rejected orders as they're processed, but with our limited remaining currency we've successfully picked up a couple of desktop wallpapers and a 3DS HOME Theme download; in each case we got the relevant codes and files right away through the automated process, and the HOME Theme code redeemed as expected on our system.
It seems like someone's forgotten to click a button on the Club Nintendo service, so we suggest acting fast if you've got leftover stars and want to spend them.
Thanks to DoctorOverbuild for the heads up.