We tried really hard to keep characters out of our house. We were completely TV free for a long time but in the last couple of years we allow DVD's. And we've been to Disney a bunch of times so they know the Disney characters rather well.
DS loves, loves, loves superheroes... I have no idea how/why. But he loves them and DH taught them which was which.
DD loves pretty much all things Disney (we stick to the classics only... Bambi and Dumbo and the like) and Hello Kitty.
We talk about "tricky advertising" and we evaluate the product and compare prices - so they get that the same item might cost more with a picture on it. They will point out how they're trying to trick you to give them your money.
I can't say I'm totally immune. I have a Disney purse (it's a nice one, for grown-ups!) and some Minnie Mouse earrings, and a stuffed Chesire Cat given me by the husband. DD has a Hello Kitty lunchbox and roll-on suitcase, and some HK memorabilia, and one of her favorite stuffies is a Minnie Mouse (who lives with her Waldorf dolls). DS has a few superhero pajamas that I found at the thrift store. He LIVES in them. He also has a Batman costume in the dress-up box, and was Spiderman for Halloween, and has a Spiderman pencil case. They both have a couple of Disney puzzles (that are really good quality.) That's about it. I will NOT allow it on furniture, bedding, going-out clothes (at-home lounge wear is OK), etc. Our books are classics, not merchandised character books, because those are usually cruddy quality storywise. They can have it on their tooth brushing cups but I did not buy the $15 Hello Kitty toothbrush for DD even though she was crying for it - she got the $1 star toothbrush because of the massive price difference. Food, we don't really buy processed food so that's kind of a non-issue.
I dunno, it's a case by case basis thing. A few touches here and there... meh, whatever. It's aesthetic preference for the most part, and if the price/quality is about the same, a few touches isn't going to kill the house. But I'm not going to go overboard with it all. And some characters I wouldn't have in our house no matter WHAT. Like Dora. Or the Bratz. Etc.