Actually, the Jessica dress thing is pretty much a myth, depending on whether you believe the animators. The scene in question is when she and Eddie Valiant get thrown from the toon car. As she is spinning around, there is a frame or two where the angle is right to see up her dress, but the animators just made it darker so that you can't really see anything. It was nighttime, after all. Some have taken this darker bit for something else, obviously....
Something that is not a myth is right at the beginning of the movie, where Roger goofs his line in the opening cartoon, and Baby Herman storms off the set. He pushes a woman's dress out of the way and storms off between her legs, startling her. Just as he emerges from the dress, you can see that his middle finger is extended. That little joke was cut out when they remastered the movie for the latest laserdisc version that was put out a few years ago. The finger is missing in all later versions, including the DVD. There was a bit of a protest from the film-enthusiast crowd because of the studio editing the movie from its original form.
I guess I'm too big of a film enthusiast for my own good. [:)]