Depends on the DLC. Some is ok (Fallout 3 is actually a decent example. So is SOME of the DLC for Oblivion. And LittleBigPlanet has good DLC. Force Unleashed DLC I plan to buy, but it's more expensive than I think it should be)
Other DLC is stupid. Examples being "We actually put this on the game disc, but you need to pay us more money to unlock it" (Soulcalibur 4, I'm looking at you here), and "Pay money to unlock stuff instead of playing the game" - although that just annoys me because buying them is stupid. I shouldn't mind as long as stupid people continue to exist and help fund the companies enabling my gaming habit, I guess...