Like anything else, if it represents good value, it's something I want and it's for a game I like, I'll probably buy it. I don't boycott "shady" practices like, say, on-disc content that's locked away with a tiny DLC key file, I just won't buy it until it's really cheap. Oh yeah, the fact that I'm a PC gamer probably helps - DLC that I wouldn't touch with a bargepole because of being too expensive is often cut in price so much that I end up buying it with store credit I get from selling trading cards.
What I really, really can't stand is the reaction some people have to DLC announcements sometimes. Payday 2 has had a lot of DLC, a lot of free updates and content too, yet every time they announce or release a new DLC you see comments that are basically saying the content should be free and that Overkill are just greedy... Yeah, because I'm sure the people who worked on that content would agree that they should work for free because they released a game like two years ago. I mean, ok, it's on me for reading the comments but still, some people are beyond parody.