Cinematics

Well ... yeah, the class announcement trailers are done using nothing but in-game assets. They're essentially Diablo III machinima if you want to classify it. And they're effing amazing. Obviously they're not the pre-rendered cinematics, but if anyone is even confused about that... then that's pretty cool too actually.

Q u o t e:
Bashiok can you confirm the presence of in-game cutscenes or does that steal from the game as the previous character dialogues as seen in the first gameplay video and that have since been removed?

The reason why those close-up character dialogues with the animated portraits were removed was because it took you away from your character and the game. So I'd be really surprised if we had in-game cinematics, but ... never say never.