Megan Garber interviews Randall Munroe, the man behind XKCD:

[L]ast year, I did a chart of money and all these different amounts of money and all the different amounts of money in the world and how they compare to each other. It was about a month and a half of sixteen-hour days of research. I had easily ten times as many academic journal articles and sources on that one comic than on anything I did in the course of my physics degree. And the comic was so large, it wound up being a huge, sprawling grid. It was sort of disorganized — I was going for this "Where's Waldo?" feel, where you could look through it, and find all this different stuff here and there. We printed up a version that was normal poster size, 24 x 36 inches, and then we got a billboard printer to make a double size version that was like six feet high, just so you could read all the little text.

That was a fun one. I don't really know about the "what is and what isn't a comic?" debate, but it's quite a stretch to call that a comic.