Following the announcement that Club Nintendo will be shutting down, Nintendo announced a schedule for the gradual discontinuation of service.
The shut down of services began on January 20. New products released after this date are no longer eligible for registration with Club Nintendo. Titles such as Hyrule Warriors that were released before this date still can be registered, though.
Nintendo will likely stop putting the Club Nintendo cards with registration codes inside of these older games, but many of the units have already been produced and will contain the registration code.
The last day that users can earn coins, either by registering games or completing surveys, will be March 31. At that time, Club Nintendo will also stop accepting new accounts.
If you've been saving up coins, you can still use them until June 30, 11:59pm PST. Thereafter, the Club Nintendo program will completely shut down, and you won't even be able to access your account.
The bright side is that Nintendo announced that it will start a new rewards program sometime after Club Nintendo shuts down, but there are no details yet about how this program will work. Nintendo did say that remaining rewards balances will not be transferable from Club Nintendo to the new program, so you should use saved up coins or stars while you have the chance.
The good news is that Club Nintendo will be giving free loyalty gifts out to users who qualified for Elite or Platinum status. These rewards will come between April 1 and April 30, which is earlier than in previous years. When they're announced, you'll be able to view reward options on Club Nintendo's website.