So, that Darkrai event I mentioned here. Turns out it is Platinum only.
In addition, Platinum players can also download Oak's Letter. This item will let people get to Flower Paradise, where Shaymin lives. It will not activate the Glacidea Flower Key Item so Shaymin can change into its Sky Forme. This Shaymin, if you can obtain the said Key Item, will change into Sky Forme.
On the Ranger front, in the UK and US, the Darkrai Mission is available to download over the Wi-Fi. It's available till Januaray 31st of 2009. You can't start the mission until you're rank 10, but once you complete the mission, you can send Darkrai into your Diamond or Pearl game once.
Finally, on the Mystery Dungeon (Time and Darkness) front, two new missions to recruit Riolu and Burmy. You receive items for you time as well (Poison Jab, Hyper Beam, Courage Dust, and Steel Dust).
That's all. Anything thing else?