There is not stigma attached to reading Manga in Japan; businessmen can regularly be seen reading them on trains. In fact, Manga is one of the most successful forms of entertainment in Japan. It earns multiple billions of dollars in a single years.
Manga is typically separated into titles for boys (shonen) and for girls (shojo). Of course, the lines often blur and women can be avid fans of shonen titles and vice versa. There is, however, a very clear delineation between books for adults and children. Manga comics for the younger crowd focus on high school drama, super heroes, and adventure. Adult comics are often complicated dramas, very violent, are sexually graphic.
Most manga are not published as a single issue, but are rather serialized in anthology magazines which feature several different stories which are released simultaneously. Stories that are popular will be released as one collected story in trade paperback format. Some will even be licensed into either animated television shows or movies.
The influence of Manga can be seen in books, movies, and television. In fact, "Avatar" director James Cameron is planning to make a live-action film based off of the classic Manga title "Battle Angel Alita."
Manga has become a part of not just Japanese pop culture, but American pop culture as well. And it looks like it is here to stay.