As the title says,
today is the final day of Kindle Store support for:
Kindle 2 (International)
Kindle DX (International)
Kindle 3 (aka Kindle Keyboard)
Kindle 4 (aka K4NT)
After the servers shut down later today,
you will still be able to download books, doing so via "View Archived Items" and having books delivered to one of these devices on Amazon's website.

Look at
https://www.amazon.com/OldKindleFAQ for more information.
I also went through the extra effort of taking screenshots of the end of support messages, as seen on my Kindle 4 (Black), but they exceed the forum's image size rules.
Edit: It has officially shut down now.
Edit 2: I have added the screenshots as attachments.