Most of you reading this won't be affected by this at all if you're a 3DS owner, but for the few who have stuck with their DSi, you'll no longer be able to access the DSi Shop after today. That's right, it's closing... forever.
While that's unfortunate news for DSi owners, there hasn't been any new games on the DSi Shop for quite a while now, and most DSi games are now also being sold on the 3DS eShop. However, there are a few that are not being sold there, such as Oregon Trail; this could be because either the original publisher is no longer around or because they haven't extended the license to include 3DS eShop sale as well.
In any case, if there are any DSi games you want specifically on your DSi, today is the last day to do it. However, you'll have a little while longer after today to continue re-downloading games you have already bought on DSi; Nintendo has said they'll end that functionality as well but will announce the end date at a later point.
If you own a 3DS, you're in the clear and will be able to continue buying most DSiware games on the 3DS eShop (and playing them on 3DS).
Also, real talk -- the DSi Shop music was GREAT if you've never listened to it before. It's sort of a remixed version of the Wii Shop Channel theme; you can check it below.
Are you sad to see the DSi Shop go?