I came to know from a reliable source some informations about Pokémon X and Pokémon Y. I have no proof of the truth of what I heard though. Mostly informations about moves, pokémon and some fragments of gameplay. I will be happy to share with you those "leaks", personally I believe without doubts, but I can understand if some of you don't. About the source, I can only tell that he's a friend of mine (obviously) and he doesn't actually work for Nintendo but he is in a position that allows him to catch informations.

I will start with some minor leaks, then you will need to ask for them:

-There are very few HMs: the HMs are Rock Smash, Surf, Strenght, Dive and another unknown to me. Moves like Waterfall and Fly are still widely usable outside battles, but aren't considered as HM.
-TMs do not break when used
-There are some moves with particular effects: there is a fire type move SE against water, a psychic type move SE against dark and many others. There are also many moves like Scald, which now gives Water STAB but acts like a fire type move. Some moves gains their type and/or effects from the Pokémon which is using them and some other moves change with evolution. In example Scyther can now learn Fly, but if Scyther evolves into Scizor Fly will inevitably turn into a new move that heals status ailments.
-Team Flare doesn't have goals but earn money
-Fire types resist fairy type moves.
-The games are set 5 years after the events of Pokémon Black 2/White 2.
-There are many references to Unova but the region isn't reachable in X and Y.
-Clemont is the ghost gym leader, Grant is the rock gym leader.
-Oorotto is Ghost/Grass type, and it has two eyes, while I saw it with one eye in many drawings pretty close to it in this board.
-The pic related I made shows the relations between the starters.

I gotta go now, I'll be back soon. Ask while I'm away.