See, I'm one of the people on the other side of the fence. I don't like having the person who wants the photo in the photo with me. It makes me feel like I'm a Disney mascot. It really isn't common at most of the cons I go to, it's so rare that when it does happen it feels weird. More often than not, the person is a) not in costume themselves, and b ) very clearly not used to being at a convention around all these people in costumes. In fact, most of the people who tend to ask to be in photos with me tend to be people who aren't even at the con - civilians, who just happened to see me going to get food or walking to the hotel or something, and are so tickled that they want a photo. They're the kinds of people who never go to cons so they don't know the subculture, they're used to taking photos of costumes at places like Disneyworld, where people in costumes are as much objects to be taken photos WITH rather than OF, much the same as a prop from a movie or a sign they find cute or what have you. I vaguely tolerate it from the mundanes because I know that's what they're used to, I'm a tourist attraction to them. So, when I get it from people at the con, it just feels weird.
I've never denied a person such a photo but I do very much dislike it. I'm used to posing in character, posing to show off the costume and/or the character. It's very hard to do that with some guy in a Batman t-shirt mugging for the camera and making V-signs next to me. And I really don't like people touching me, so if they go for the arm-around I'm right out.
So...yes, people DO find it creepy. But not all people. I just don't understand the point because that's not my goal in costume photography. When I take photos, I want to preserve my memory of that costume. Having me in the shot would ruin it. It's not to say that if you want to be in the photo's that's wrong, but I thought I'd chime in since I do hold a different opinion and I want to let folks know that we do exist.
Founder and President, Madison Area Costuming Society, a chapter of the International Costumer's Guild
Strange Land Costuming - www.strangelandcostumes.com