Mostly about how and when they activate. Obviously when you switch your pokemon in, their ability takes effect.
But what if I have a pokemon with Rivalry. He gets sent out against another Male pokemon, and thus raises his attack. The other trainer switches out to a female pokemon. Does the Attack boost remain, or does it silently drop?
Does Intimidate silently lower the attack of pokemon who switch in, or is it ONLY when I switch MY pokemon in who has it?
Maybe I'm still just braindead from the con.