Unlikely in the sense that you would never guess from a film like 'Ghost World' or HOV that it came from a graphic novel. They've been an unsually fruitful source for very good films.
Ghost World, with Steve Buscemi and that dorky girl was from a comic book? Saw it on IFC and never would have guessed.
SD
I guess if you're not big into the graphic novel world that makes sense. Comics haven't just been for kids for a while (really since Miller resurected Batman with Darknight), it is a pretty fertile ground, but one that's been going largely unnoticed by the non-geek crowd until recently. When Spiderman and X-Men made all that fat cash though it sent the Hollywood guys running to the comic book store in a desperate search for more licenses to print money though. IMHO a good thing, overall I think the comic book movies have been of pretty solid quality (with a few glaring exceptions).