This LA Times article is a good snapshot of the issues associated with comic books getting scanned and shared online. I assume it is tough for traditional comic book publishers – from DC and Marvel down to the smaller indy shops – to sort out how to deal with this. On the one hand if online comic book file sharing is following the same trajectory as music (and now video) file sharing, it's conceivable that the audience will grow tremendously – far outstripping the current market for comic books.
The downside, of course is that all of those readers online aren't paying the $3 + for the paper comic book. Although publishers may fight this or ignore this, some smart publisher is going to figure out a way to leverage this at some point and convert a significant enough number of file sharing fans into paying fans to create a new business model for comic books. It may not wind up being all that different from evolving efforts by webcomic creators but I don't doubt that it's coming.