I used to really support it, but lately, I'm just so completely DONE with DLC. 90% of the DLC that gets slapped out nowadays just gets me mad.
Here's a list of DLC practices that immediately turn me off of a game:
Day 1 DLC - If it's available on day one, why the hell couldn't you ship it with the game in the first place?
Retailer-exclusive/timed exclusive DLC - You know, when I buy a game, especially a game where I might want to get everything in it, NOTHING is more annoying than finding out that certain content is no longer available, or it was ONLY available if you bought the game from a certain retailer. I GET that this is supposed to make people buy the games on launch day, and dissuade them from buying used, but what if, a year or two down the line, you want to buy a certain game, but now some content on that game is PERMANENTLY beyond your grasp? Double points if there are different DLC packs for different retailers.
On-Disc DLC - I. Fucking. HATE this. If that content is on the freaking disc, then by all accounts, I should be able to access it. I bought the game. I have it in my hands. The code for said content is literally a part of the disc that I own... except it's not unless I pay them MORE money. I'll be blunt, anyone who REFUSES to pay for on-disc DLC, and instead hacks the game to get it, I have no ill will towards you.
Content that sections off large parts of the main game - I'm looking at you, Catwoman story in Arkham City. You had NO business being DLC. Sure, I got you for free, but see my second point.
Now, on the flip side, here are DLC practices that I'm okay with:
Vanity items - No issues here. Not integral to beating the game, and you're probably not missing anything if you don't get it. HOWEVER, in games where vanity items are a large part of the game, there had DAMN WELL better be alot of it that I can freely unlock myself before I feel the need to start digging into the DLC. LittleBig Planet is a good example. Yeah, there's tons of DLC costumes, but there's a metric ton of costume options to unlock in the main game.
Expansion pack-styled DLC - The recent Fallouts, Skyrim, Borderlands, World of Warcraft, all of these are perfectly acceptable, as they're actually charging you for stuff that REALLY adds to your play experience.
Paying to unlock stuff in main game - Doesn't happen often, but I have no issue with the idea of paying money to unlock stuff in your own game. Granted, I wound never actually USE it, but having the option doesn't bother me. The upcoming powerleveling to 90 that WoW is going to do is an example of this that I'm okay with.