PAX East 2012 (or, the "Penny Arcade Expo") is a gaming event in Boston that ran between April 6 to April 8, 2012. While Kingdom Hearts 3D [Dream Drop Distance] was not on Square Enix's line-up of games for the event, it did actually appear with some small coverage. Firstly, we have a nice image of a Kingdom Hearts 3D cube below, which appeared at the event. This was uploaded by SquareEnixEmily.
Secondly, thanks to GameZone, we know that Kingdom Hearts 3D appeared at the event with a demo entirely in Japanese. Hopefully, we'll see some English demos later on, but if you would like to read impressions of the Japanese demo then read on. This Kingdom Hearts 3D demo was press-only, and not playable by members of the public.
GameZone's impressions of the Kingdom Hearts 3D demo
The Game Fanatic's impressions of the Kingdom Hearts 3D demo
Game Rant's impressions of the Kingdom Hearts 3D demo
Destructoid's impressions of the Kingdom Hearts 3D demo
Escapist Magazine's impressions of the Kingdom Hearts 3D demo
Update: If you read The Game Fanatic's impressions of the demo, then you might notice the following excerpt:
How interesting! It seems that Square Enix are preparing an English demo for Kingdom Hearts 3D. It sounds like this will most likely be a press-only demo as well, but who knows, if we're lucky then we might see the demo elsewhere!