Conceptually, DLC is not really different from the expansion packs back in the day. How it is used to get the absolute maximum amount of money out of every single title, however, is pretty sickening. Intentionally reducing the content of the base game in order to sell it as optional extras makes the game community poorer. There's less common ground for people when they talk about their games, as each player could in the worst case scenario end up with two entirely different playing experiences.

Player A (who bought the day one DLC and preorder bonus with 5 extra weapons and an additional character): I loved player as OtherDude. Game was a bit easy, though.
Player B (just got the base game): Uh, I dunno what you're on about. It was pretty difficult for me. I found the character to be pretty boring too.

I refuse to pay extra for any DLC that is designed while the game is still being developed. This includes preorder bonuses and "digital collector's edition (what a smurfing horsetrout concept that is)" bonuses, as these are just day one DLC in disguise. I'll grab them as part of a "goty" or "complete edition" for 40 bucks the next year, however.