Single Status Update
Basically, anything to do with the leak. Stuff that was obviously never planned to be shown. In other words, stuff that has not been shown in advertising, etc.
Whenever a new 'generation' comes out, half of the fun for me is discovering all the new Pokemon. So if someone came along and showed me a complete list of the new Pokemon, the urge to punch them in the face would be very high.
Granted, Game Freak have been advertising a lot of new Pokemon, but I still believe there's some that they wanted to hold back. Those would be spoilers to me.
Although it could just be me, some people might like to know all of the Pokemon before hand.